How to use Reflection in FluentValidation?

How to use Reflection in FluentValidation? - c#

I have a scneario in which I want to use reflection to do validation using FluentValidation. Someting like this:
public class FooValidator : AbstractValidator<Foo>
{
public FooValidator(Foo obj)
{
// Iterate properties using reflection
var properties = ReflectionHelper.GetShallowPropertiesInfo(obj);
foreach (var prop in properties)
{
// Create rule for each property, based on some data coming from other service...
//RuleFor(o => o.Description).NotEmpty().When(o => // this works fine when foo.Description is null
RuleFor(o => o.GetType().GetProperty(prop.Name)).NotEmpty().When(o =>
{
return true; // do other stuff...
});
}
}
}
The call to ReflectionHelper.GetShallowPropertiesInfo(obj) returns "shallow" properties of object. Then, for each property I create a rule.
This is my code for get properties of object:
public static class ReflectionHelper
{
public static IEnumerable<PropertyInfo> GetShallowPropertiesInfo<T>(T o) where T : class
{
var type = typeof(T);
var properties =
from pi in type.GetProperties(BindingFlags.Public | BindingFlags.Instance)
where pi.PropertyType.Module.ScopeName == "CommonLanguageRuntimeLibrary"
&& !(pi.PropertyType.IsGenericType && pi.PropertyType.GetGenericTypeDefinition() == typeof(ICollection<>))
select pi;
return properties;
}
}
This code compile and can be executed
IValidator<Foo> validator = new FooValidator(foo);
var results = validator.Validate(foo);
But it doesn't work properly (validation never fails). Is there any way to achieve this?
Note: Demo code can be found int Github at FluentValidationReflection

Finally I've found a solution that works. I've created a custom PropertyValidator that receives a PropertyInfo parameter:
public class CustomNotEmpty<T> : PropertyValidator
{
private PropertyInfo _propertyInfo;
public CustomNotEmpty(PropertyInfo propertyInfo)
: base(string.Format("{0} is required", propertyInfo.Name))
{
_propertyInfo = propertyInfo;
}
protected override bool IsValid(PropertyValidatorContext context)
{
return !IsNullOrEmpty(_propertyInfo, (T)context.Instance);
}
private bool IsNullOrEmpty(PropertyInfo property, T obj)
{
var t = property.PropertyType;
var v = property.GetValue(obj);
// Omitted for clarity...
}
}
And a extension method for IRuleBuilder:
public static class ValidatorExtensions
{
public static IRuleBuilderOptions<T, T> CustomNotEmpty<T>(
this IRuleBuilder<T, T> ruleBuilder, PropertyInfo propertyInfo)
{
return ruleBuilder.SetValidator(new CustomNotEmpty<T>(propertyInfo));
}
}
With this I can change my FooValidator as follows:
public class FooValidator : AbstractValidator<Foo>
{
public FooValidator(Foo obj)
{
// Iterate properties using reflection
var properties = ReflectionHelper.GetShallowPropertiesInfo(obj);
foreach (var prop in properties)
{
// Create rule for each property, based on some data coming from other service...
RuleFor(o => o)
.CustomNotEmpty(obj.GetType().GetProperty(prop.Name))
.When(o =>
{
return true; // do other stuff...
});
}
}
}
And now I'm be able to use Reflection to add rules for specific properties

For reflection i use
RuleFor(x => new obj().GetType().GetProperty(x.Filter.ColumnName)).NotNull();

Related

Accessing a Page Factory's declared Using [duplicate]

I have a class, lets call it Book with a property called Name. With that property, I have an attribute associated with it.
public class Book
{
[Author("AuthorName")]
public string Name
{
get; private set;
}
}
In my main method, I'm using reflection and wish to get key value pair of each attribute for each property. So in this example, I'd expect to see "Author" for attribute name and "AuthorName" for the attribute value.
Question: How do I get the attribute name and value on my properties using Reflection?

Use typeof(Book).GetProperties() to get an array of PropertyInfo instances. Then use GetCustomAttributes() on each PropertyInfo to see if any of them have the Author Attribute type. If they do, you can get the name of the property from the property info and the attribute values from the attribute.
Something along these lines to scan a type for properties that have a specific attribute type and to return data in a dictionary (note that this can be made more dynamic by passing types into the routine):
public static Dictionary<string, string> GetAuthors()
{
Dictionary<string, string> _dict = new Dictionary<string, string>();
PropertyInfo[] props = typeof(Book).GetProperties();
foreach (PropertyInfo prop in props)
{
object[] attrs = prop.GetCustomAttributes(true);
foreach (object attr in attrs)
{
AuthorAttribute authAttr = attr as AuthorAttribute;
if (authAttr != null)
{
string propName = prop.Name;
string auth = authAttr.Name;
_dict.Add(propName, auth);
}
}
}
return _dict;
}

To get all attributes of a property in a dictionary use this:
typeof(Book)
.GetProperty("Name")
.GetCustomAttributes(false)
.ToDictionary(a => a.GetType().Name, a => a);
remember to change from false to true if you want to include inheritted attributes as well.

If you just want one specific Attribute value For instance Display Attribute you can use the following code:
var pInfo = typeof(Book).GetProperty("Name")
.GetCustomAttribute<DisplayAttribute>();
var name = pInfo.Name;

I have solved similar problems by writing a Generic Extension Property Attribute Helper:
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
public static class AttributeHelper
{
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(
Expression<Func<T, TOut>> propertyExpression,
Func<TAttribute, TValue> valueSelector)
where TAttribute : Attribute
{
var expression = (MemberExpression) propertyExpression.Body;
var propertyInfo = (PropertyInfo) expression.Member;
var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() as TAttribute;
return attr != null ? valueSelector(attr) : default(TValue);
}
}
Usage:
var author = AttributeHelper.GetPropertyAttributeValue<Book, string, AuthorAttribute, string>(prop => prop.Name, attr => attr.Author);
// author = "AuthorName"

You can use GetCustomAttributesData() and GetCustomAttributes():
var attributeData = typeof(Book).GetProperty("Name").GetCustomAttributesData();
var attributes = typeof(Book).GetProperty("Name").GetCustomAttributes(false);

If you mean "for attributes that take one parameter, list the attribute-names and the parameter-value", then this is easier in .NET 4.5 via the CustomAttributeData API:
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;
public static class Program
{
static void Main()
{
PropertyInfo prop = typeof(Foo).GetProperty("Bar");
var vals = GetPropertyAttributes(prop);
// has: DisplayName = "abc", Browsable = false
}
public static Dictionary<string, object> GetPropertyAttributes(PropertyInfo property)
{
Dictionary<string, object> attribs = new Dictionary<string, object>();
// look for attributes that takes one constructor argument
foreach (CustomAttributeData attribData in property.GetCustomAttributesData())
{
if(attribData.ConstructorArguments.Count == 1)
{
string typeName = attribData.Constructor.DeclaringType.Name;
if (typeName.EndsWith("Attribute")) typeName = typeName.Substring(0, typeName.Length - 9);
attribs[typeName] = attribData.ConstructorArguments[0].Value;
}
}
return attribs;
}
}
class Foo
{
[DisplayName("abc")]
[Browsable(false)]
public string Bar { get; set; }
}

private static Dictionary<string, string> GetAuthors()
{
return typeof(Book).GetProperties()
.SelectMany(prop => prop.GetCustomAttributes())
.OfType<AuthorAttribute>()
.ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), a => a.Name);
}
Example using generics (target framework 4.5)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
private static Dictionary<string, string> GetAttribute<TAttribute, TType>(
Func<TAttribute, string> valueFunc)
where TAttribute : Attribute
{
return typeof(TType).GetProperties()
.SelectMany(p => p.GetCustomAttributes())
.OfType<TAttribute>()
.ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), valueFunc);
}
Usage
var dictionary = GetAttribute<AuthorAttribute, Book>(a => a.Name);

public static class PropertyInfoExtensions
{
public static TValue GetAttributValue<TAttribute, TValue>(this PropertyInfo prop, Func<TAttribute, TValue> value) where TAttribute : Attribute
{
var att = prop.GetCustomAttributes(
typeof(TAttribute), true
).FirstOrDefault() as TAttribute;
if (att != null)
{
return value(att);
}
return default(TValue);
}
}
Usage:
//get class properties with attribute [AuthorAttribute]
var props = typeof(Book).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(AuthorAttribute)));
foreach (var prop in props)
{
string value = prop.GetAttributValue((AuthorAttribute a) => a.Name);
}
or:
//get class properties with attribute [AuthorAttribute]
var props = typeof(Book).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(AuthorAttribute)));
IList<string> values = props.Select(prop => prop.GetAttributValue((AuthorAttribute a) => a.Name)).Where(attr => attr != null).ToList();

While the above most upvoted answers definitely work, I'd suggest using a slightly different approach in some cases.
If your class has multiple properties with always the same attribute and you want to get those attributes sorted into a dictionary, here is how:
var dict = typeof(Book).GetProperties().ToDictionary(p => p.Name, p => p.GetCustomAttributes(typeof(AuthorName), false).Select(a => (AuthorName)a).FirstOrDefault());
This still uses cast but ensures that the cast will always work as you will only get the custom attributes of the type "AuthorName".
If you had multiple Attributes above answers would get a cast exception.

Here are some static methods you can use to get the MaxLength, or any other attribute.
using System;
using System.Linq;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;
public static class AttributeHelpers {
public static Int32 GetMaxLength<T>(Expression<Func<T,string>> propertyExpression) {
return GetPropertyAttributeValue<T,string,MaxLengthAttribute,Int32>(propertyExpression,attr => attr.Length);
}
//Optional Extension method
public static Int32 GetMaxLength<T>(this T instance,Expression<Func<T,string>> propertyExpression) {
return GetMaxLength<T>(propertyExpression);
}
//Required generic method to get any property attribute from any class
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(Expression<Func<T,TOut>> propertyExpression,Func<TAttribute,TValue> valueSelector) where TAttribute : Attribute {
var expression = (MemberExpression)propertyExpression.Body;
var propertyInfo = (PropertyInfo)expression.Member;
var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute),true).FirstOrDefault() as TAttribute;
if (attr==null) {
throw new MissingMemberException(typeof(T).Name+"."+propertyInfo.Name,typeof(TAttribute).Name);
}
return valueSelector(attr);
}
}
Using the static method...
var length = AttributeHelpers.GetMaxLength<Player>(x => x.PlayerName);
Or using the optional extension method on an instance...
var player = new Player();
var length = player.GetMaxLength(x => x.PlayerName);
Or using the full static method for any other attribute (StringLength for example)...
var length = AttributeHelpers.GetPropertyAttributeValue<Player,string,StringLengthAttribute,Int32>(prop => prop.PlayerName,attr => attr.MaximumLength);
Inspired by the Mikael Engver's answer.

I wrote this into a dynamic method since I use lots of attributes throughout my application. Method:
public static dynamic GetAttribute(Type objectType, string propertyName, Type attrType)
{
//get the property
var property = objectType.GetProperty(propertyName);
//check for object relation
return property.GetCustomAttributes().FirstOrDefault(x => x.GetType() == attrType);
}
Usage:
var objectRelAttr = GetAttribute(typeof(Person), "Country", typeof(ObjectRelationAttribute));
var displayNameAttr = GetAttribute(typeof(Product), "Category", typeof(DisplayNameAttribute));
Hope this helps anyone

Necromancing.
For those that still have to maintain .NET 2.0, or those that want to do it without LINQ:
public static object GetAttribute(System.Reflection.MemberInfo mi, System.Type t)
{
object[] objs = mi.GetCustomAttributes(t, true);
if (objs == null || objs.Length < 1)
return null;
return objs[0];
}
public static T GetAttribute<T>(System.Reflection.MemberInfo mi)
{
return (T)GetAttribute(mi, typeof(T));
}
public delegate TResult GetValue_t<in T, out TResult>(T arg1);
public static TValue GetAttributValue<TAttribute, TValue>(System.Reflection.MemberInfo mi, GetValue_t<TAttribute, TValue> value) where TAttribute : System.Attribute
{
TAttribute[] objAtts = (TAttribute[])mi.GetCustomAttributes(typeof(TAttribute), true);
TAttribute att = (objAtts == null || objAtts.Length < 1) ? default(TAttribute) : objAtts[0];
// TAttribute att = (TAttribute)GetAttribute(mi, typeof(TAttribute));
if (att != null)
{
return value(att);
}
return default(TValue);
}
Example usage:
System.Reflection.FieldInfo fi = t.GetField("PrintBackground");
wkHtmlOptionNameAttribute att = GetAttribute<wkHtmlOptionNameAttribute>(fi);
string name = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, delegate(wkHtmlOptionNameAttribute a){ return a.Name;});
or simply
string aname = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, a => a.Name );

Just looking for the right place to put this piece of code.
let's say you have the following property:
[Display(Name = "Solar Radiation (Average)", ShortName = "SolarRadiationAvg")]
public int SolarRadiationAvgSensorId { get; set; }
And you want to get the ShortName value. You can do:
((DisplayAttribute)(typeof(SensorsModel).GetProperty(SolarRadiationAvgSensorId).GetCustomAttribute(typeof(DisplayAttribute)))).ShortName;
Or to make it general:
internal static string GetPropertyAttributeShortName(string propertyName)
{
return ((DisplayAttribute)(typeof(SensorsModel).GetProperty(propertyName).GetCustomAttribute(typeof(DisplayAttribute)))).ShortName;
}

foreach (var p in model.GetType().GetProperties())
{
var valueOfDisplay =
p.GetCustomAttributesData()
.Any(a => a.AttributeType.Name == "DisplayNameAttribute") ?
p.GetCustomAttribute<DisplayNameAttribute>().DisplayName :
p.Name;
}
In this example I used DisplayName instead of Author because it has a field named 'DisplayName' to be shown with a value.

to get attribute from enum, i'm using :
public enum ExceptionCodes
{
[ExceptionCode(1000)]
InternalError,
}
public static (int code, string message) Translate(ExceptionCodes code)
{
return code.GetType()
.GetField(Enum.GetName(typeof(ExceptionCodes), code))
.GetCustomAttributes(false).Where((attr) =>
{
return (attr is ExceptionCodeAttribute);
}).Select(customAttr =>
{
var attr = (customAttr as ExceptionCodeAttribute);
return (attr.Code, attr.FriendlyMessage);
}).FirstOrDefault();
}
// Using
var _message = Translate(code);

If you want get property having the custom Attribute then please try the following:
IEnumerable propertyInfos = properties.GetType().GetProperties();
PropertyInfo p = propertyInfos.Where(x => x.GetCustomAttribute() != null);

Using reflection on generics recursively

I have the following classes:
public class BaseDataEntity
{
private List<string> _Changes = new List<string>();
public IEnumerable<string> GetChanges()
{
return _Changes;
}
public bool HasDataChanged
{
get { return (GetChanges().Count() > 0); }
}
public bool HasChildRecords
{
get { return (GetType().GetChildRecords().Count() > 0); }
}
}
public class ChildRecords : IList<T> where T : BaseDataEntity
{
}
And a few helper methods:
public static PropertyInfo[] GetChildRecords(this Type aType)
{
return aType.GetProperties().Where(pi => pi.IsChildRecords()).ToArray();
}
public static bool IsChildRecords(this PropertyInfo info)
{
return (info.GetCustomAttributes(typeof(ChildRecordsAttribute), false).Length > 0);
}
What I'm trying to do is implement a property called HaveChildRecordsChanged using reflection. My question is how would I go about using reflection to check the HasDataChanged property of all ChildRecords of arbitrary depth?
I tried something like:
var isChanged = false;
foreach (var info in GetType().GetChildRecords())
{
var childRecordObject = info.GetValue(this, null);
var childRecords = childRecordObject as ChildRecords<BaseDataEntity>; //cannot unbox this, it evaluates as null
if (null != childRecords && childRecords.Any(x => x.HasDataChanged))
{
isChanged = true; //never hit
}
}
return isChanged;

ChildRecords<T> is generic so ChildRecords<Company> can't be cast to ChildRecords<BaseDataEntity>.
Since you already filter the property marked with the ChildRecordsAttribute the simplest solution would be to cast to IEnumerable and use OfType<BaseDataEntity>()
var childRecords = childRecordObject as IEnumerable; // IList<T> will be IEnumerable
if (null != childRecords && childRecords.OfType<BaseDataEntity>().Any(x => x.HasDataChanged))
{
isChanged = true;
}

How to get methods with "Priority" attribute value [duplicate]

I need to be able to read the value of my attribute from within my Method, how can I do that?
[MyAttribute("Hello World")]
public void MyMethod()
{
// Need to read the MyAttribute attribute and get its value
}

You need to call the GetCustomAttributes function on a MethodBase object.
The simplest way to get the MethodBase object is to call MethodBase.GetCurrentMethod. (Note that you should add [MethodImpl(MethodImplOptions.NoInlining)])
For example:
MethodBase method = MethodBase.GetCurrentMethod();
MyAttribute attr = (MyAttribute)method.GetCustomAttributes(typeof(MyAttribute), true)[0] ;
string value = attr.Value; //Assumes that MyAttribute has a property called Value
You can also get the MethodBase manually, like this: (This will be faster)
MethodBase method = typeof(MyClass).GetMethod("MyMethod");

[MyAttribute("Hello World")]
public int MyMethod()
{
var myAttribute = GetType().GetMethod("MyMethod").GetCustomAttributes(true).OfType<MyAttribute>().FirstOrDefault();
}

The available answers are mostly outdated.
This is the current best practice:
class MyClass
{
[MyAttribute("Hello World")]
public void MyMethod()
{
var method = typeof(MyClass).GetRuntimeMethod(nameof(MyClass.MyMethod), Array.Empty<Type>());
var attribute = method.GetCustomAttribute<MyAttribute>();
}
}
This requires no casting and is pretty safe to use.
You can also use .GetCustomAttributes<T> to get all attributes of one type.

If you store the default attribute value into a property (Name in my example) on construction, then you can use a static Attribute helper method:
using System;
using System.Linq;
public class Helper
{
public static TValue GetMethodAttributeValue<TAttribute, TValue>(Action action, Func<TAttribute, TValue> valueSelector) where TAttribute : Attribute
{
var methodInfo = action.Method;
var attr = methodInfo.GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() as TAttribute;
return attr != null ? valueSelector(attr) : default(TValue);
}
}
Usage:
var name = Helper.GetMethodAttributeValue<MyAttribute, string>(MyMethod, x => x.Name);
My solution is based on that the default value is set upon the attribute construction, like this:
internal class MyAttribute : Attribute
{
public string Name { get; set; }
public MyAttribute(string name)
{
Name = name;
}
}

In case you are implementing the setup like #Mikael Engver mentioned above, and allow multiple usage. Here is what you can do to get the list of all the attribute values.
[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public class TestCase : Attribute
{
public TestCase(string value)
{
Id = value;
}
public string Id { get; }
}
public static IEnumerable<string> AutomatedTests()
{
var assembly = typeof(Reports).GetTypeInfo().Assembly;
var methodInfos = assembly.GetTypes().SelectMany(m => m.GetMethods())
.Where(x => x.GetCustomAttributes(typeof(TestCase), false).Length > 0);
foreach (var methodInfo in methodInfos)
{
var ids = methodInfo.GetCustomAttributes<TestCase>().Select(x => x.Id);
yield return $"{string.Join(", ", ids)} - {methodInfo.Name}"; // handle cases when one test is mapped to multiple test cases.
}
}

I used this method :
public static TAttributeMember? GetMethodAttributeValue<TAttribute, TAttributeMember>(Expression<Func<object>> property, Func<TAttribute, TAttributeMember> valueSelector) where TAttribute : Attribute
{
var methodInfo = ((MemberExpression)property.Body).Member as PropertyInfo;
var attr = methodInfo?.GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() as TAttribute;
return attr != null && valueSelector != null ? valueSelector(attr) : default(TAttributeMember);
}
Then can use like this:
var group = GetMethodAttributeValue<FieldAttribs, FieldGroups>(() => dd.Param2, a => a.Group);

Map database column to constant value without the need for a property in the entity class

Is it possible to map a database column to a constant value without the need for a property in the entity class? This basically is a workaround for a missing default value on that column in the database in combination with a NOT NULL constrained. The database is external and can't be changed but I don't need all of the columns in that table and thus don't want to have corresponding properties in my entity class.
I am asking basically the same as described in this Hibernate JIRA issue.

Based on Firos answer I solved the problem. However, I didn't quite like the syntax to be used and the fact that I would have to create a new class for the default values for each entity.
The syntax I got now looks like this:
mapping.ConstantValue(0).Column(#"client_id");
// or
mapping.ConstantValue(0, #"client_id");
I created the following extension methods for it:
public static PropertyPart
ConstantValue<TType, TValue>(this ClasslikeMapBase<TType> map, TValue value)
{
var getter =
new ConstantValueGetter<TValue>(CreateUniqueMemberName(), value);
ConstantValueAccessor.RegisterGetter(typeof(TType), getter);
var propertyInfo =
new GetterSetterPropertyInfo(typeof(TType), typeof(TValue),
getter.PropertyName, getter.Method, null);
var parameter = Expression.Parameter(typeof(TType), "x");
Expression body = Expression.Property(parameter, propertyInfo);
body = Expression.Convert(body, , typeof(object));
var lambda = Expression.Lambda<Func<TType, object>>(body, parameter);
return map.Map(lambda).Access.Using<ConstantValueAccessor>();
}
public static PropertyPart
ConstantValue<TType, TValue>(this ClasslikeMapBase<TType> map,
TValue value, string column)
{
return map.ConstantValue(value).Column(column);
}
The important differences are:
The first of those extension methods returns a PropertyPart and has to be used in conjunction with the Column method to specify which column the constant value should be mapped to. Because of this, the column name is not known when the extension method is executed and we need to create one ourselves. This is done by CreateUniqueMemberName:
private static string CreateUniqueMemberName()
{
return "Dummy" + Guid.NewGuid().ToString("N");
}
Because you can only specify a type as access strategy and not an instance, I couldn't create an IPropertyAccessor implementation allowed me to simply pass an IGetter instance in the constructor. That's what ConstantValueAccessor.RegisterGetter(typeof(TType), getter); solves. ConstantValueAccessor has a static collection of getters:
internal class ConstantValueAccessor : IPropertyAccessor
{
private static readonly
ConcurrentDictionary<Type, SynchronizedCollection<IGetter>> _getters =
new ConcurrentDictionary<Type, SynchronizedCollection<IGetter>>();
public static void RegisterGetter(Type type, IGetter getter)
{
var getters =
_getters.GetOrAdd(type,
t => new SynchronizedCollection<IGetter>());
getters.Add(getter);
}
public IGetter GetGetter(Type theClass, string propertyName)
{
SynchronizedCollection<IGetter> getters;
if (!_getters.TryGetValue(theClass, out getters))
return null;
return getters.SingleOrDefault(x => x.PropertyName == propertyName);
}
// ...
}
The implementation of ConstantValueGetter<T> is the same as the one from the provided link.
Because it wasn't that much fun to implement GetterSetterPropertyInfo, here it is. One important difference is, that this implementation doesn't have any dependencies on (Fluent) NHibernate.

My implementation takes the same idea as hival but goes a lot further. the basis is an implementation of IPropertyAccessor
/// <summary>
/// Defaultvalues für nicht (mehr) benötigte Spalten siehe
/// http://elegantcode.com/2009/07/13/using-nhibernate-for-legacy-databases/
/// </summary>
public abstract class DefaultValuesBase : IPropertyAccessor
{
public abstract IEnumerable<IGetter> DefaultValueGetters { get; }
public bool CanAccessThroughReflectionOptimizer
{
get { return false; }
}
public IGetter GetGetter(Type theClass, string propertyName)
{
return DefaultValueGetters.SingleOrDefault(getter => getter.PropertyName == propertyName);
}
public ISetter GetSetter(Type theClass, string propertyName)
{
return new NoopSetter();
}
}
// taken from the link
[Serializable]
public class DefaultValueGetter<T> : IGetter {...}
// ---- and the most tricky part ----
public static void DefaultValues<T>(this ClasslikeMapBase<T> map, DefaultValuesBase defaults)
{
DefaultValuesInternal<T>(map.Map, defaults);
}
public static void DefaultValues<T>(this CompositeElementPart<T> map, DefaultValuesBase defaults)
{
DefaultValuesInternal<T>(map.Map, defaults);
}
private static void DefaultValuesInternal<T>(
Func<Expression<Func<T, object>>, PropertyPart> mapFunction, DefaultValuesBase defaults)
{
var noopSetter = new NoopSetter();
var defaultsType = defaults.GetType();
foreach (var defaultgetter in defaults.DefaultValueGetters)
{
var parameter = Expression.Parameter(typeof(T), "x");
Expression body = Expression.Property(parameter,
new GetterSetterPropertyInfo(typeof(T), defaultgetter, noopSetter));
body = Expression.Convert(body, typeof(object));
var lambda = Expression.Lambda<Func<T, object>>(body, parameter);
mapFunction(lambda).Column(defaultgetter.PropertyName).Access.Using(defaultsType);
}
}
// GetterSetterPropertyInfo inherits PropertyInfo with important part
public override string Name
{
get { return m_getter.PropertyName; } // propertyName is the column in db
}
// and finally in SomeEntityMap
this.DefaultValues(new SomeEntityDefaults());
public class SomeEntityDefaults : DefaultValuesBase
{
public override IEnumerable<IGetter> DefaultValueGetters
{
get
{
return new [] {
new DefaultValueGetter<int>("someColumn", 1),
new DefaultValueGetter<string>("somestrColumn", "empty"),
};
}
}
}

If you don't want to introduce property in your entity class the only solution I see is to create custom property accessor which will always return constant value. Here is possible implementation:
public class ConstantAccessor : IPropertyAccessor
{
#region IPropertyAccessor Members
public IGetter GetGetter(Type theClass, string propertyName)
{
return new ConstantGetter();
}
public ISetter GetSetter(Type theClass, string propertyName)
{
return new NoopSetter();
}
public bool CanAccessThroughReflectionOptimizer
{
get { return false; }
}
#endregion
[Serializable]
private class ConstantGetter : IGetter
{
#region IGetter Members
public object Get(object target)
{
return 0; // Always return constant value
}
public Type ReturnType
{
get { return typeof(object); }
}
public string PropertyName
{
get { return null; }
}
public MethodInfo Method
{
get { return null; }
}
public object GetForInsert(object owner, IDictionary mergeMap,
ISessionImplementor session)
{
return null;
}
#endregion
}
[Serializable]
private class NoopSetter : ISetter
{
#region ISetter Members
public void Set(object target, object value)
{
}
public string PropertyName
{
get { return null; }
}
public MethodInfo Method
{
get { return null; }
}
#endregion
}
}
Here how to use it:
<property name="Value"
access="ConsoleApplication2.ConstantAccessor, ConsoleApplication2"
column="a_value" type="int" />
Property "Value" doesn't need to exist in your entity. It is here because attribute "name" is required.

Reflection - get attribute name and value on property

I have a class, lets call it Book with a property called Name. With that property, I have an attribute associated with it.
public class Book
{
[Author("AuthorName")]
public string Name
{
get; private set;
}
}
In my main method, I'm using reflection and wish to get key value pair of each attribute for each property. So in this example, I'd expect to see "Author" for attribute name and "AuthorName" for the attribute value.
Question: How do I get the attribute name and value on my properties using Reflection?

Use typeof(Book).GetProperties() to get an array of PropertyInfo instances. Then use GetCustomAttributes() on each PropertyInfo to see if any of them have the Author Attribute type. If they do, you can get the name of the property from the property info and the attribute values from the attribute.
Something along these lines to scan a type for properties that have a specific attribute type and to return data in a dictionary (note that this can be made more dynamic by passing types into the routine):
public static Dictionary<string, string> GetAuthors()
{
Dictionary<string, string> _dict = new Dictionary<string, string>();
PropertyInfo[] props = typeof(Book).GetProperties();
foreach (PropertyInfo prop in props)
{
object[] attrs = prop.GetCustomAttributes(true);
foreach (object attr in attrs)
{
AuthorAttribute authAttr = attr as AuthorAttribute;
if (authAttr != null)
{
string propName = prop.Name;
string auth = authAttr.Name;
_dict.Add(propName, auth);
}
}
}
return _dict;
}

To get all attributes of a property in a dictionary use this:
typeof(Book)
.GetProperty("Name")
.GetCustomAttributes(false)
.ToDictionary(a => a.GetType().Name, a => a);
remember to change from false to true if you want to include inheritted attributes as well.

If you just want one specific Attribute value For instance Display Attribute you can use the following code:
var pInfo = typeof(Book).GetProperty("Name")
.GetCustomAttribute<DisplayAttribute>();
var name = pInfo.Name;

I have solved similar problems by writing a Generic Extension Property Attribute Helper:
using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
public static class AttributeHelper
{
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(
Expression<Func<T, TOut>> propertyExpression,
Func<TAttribute, TValue> valueSelector)
where TAttribute : Attribute
{
var expression = (MemberExpression) propertyExpression.Body;
var propertyInfo = (PropertyInfo) expression.Member;
var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() as TAttribute;
return attr != null ? valueSelector(attr) : default(TValue);
}
}
Usage:
var author = AttributeHelper.GetPropertyAttributeValue<Book, string, AuthorAttribute, string>(prop => prop.Name, attr => attr.Author);
// author = "AuthorName"

You can use GetCustomAttributesData() and GetCustomAttributes():
var attributeData = typeof(Book).GetProperty("Name").GetCustomAttributesData();
var attributes = typeof(Book).GetProperty("Name").GetCustomAttributes(false);

If you mean "for attributes that take one parameter, list the attribute-names and the parameter-value", then this is easier in .NET 4.5 via the CustomAttributeData API:
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;
public static class Program
{
static void Main()
{
PropertyInfo prop = typeof(Foo).GetProperty("Bar");
var vals = GetPropertyAttributes(prop);
// has: DisplayName = "abc", Browsable = false
}
public static Dictionary<string, object> GetPropertyAttributes(PropertyInfo property)
{
Dictionary<string, object> attribs = new Dictionary<string, object>();
// look for attributes that takes one constructor argument
foreach (CustomAttributeData attribData in property.GetCustomAttributesData())
{
if(attribData.ConstructorArguments.Count == 1)
{
string typeName = attribData.Constructor.DeclaringType.Name;
if (typeName.EndsWith("Attribute")) typeName = typeName.Substring(0, typeName.Length - 9);
attribs[typeName] = attribData.ConstructorArguments[0].Value;
}
}
return attribs;
}
}
class Foo
{
[DisplayName("abc")]
[Browsable(false)]
public string Bar { get; set; }
}

private static Dictionary<string, string> GetAuthors()
{
return typeof(Book).GetProperties()
.SelectMany(prop => prop.GetCustomAttributes())
.OfType<AuthorAttribute>()
.ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), a => a.Name);
}
Example using generics (target framework 4.5)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
private static Dictionary<string, string> GetAttribute<TAttribute, TType>(
Func<TAttribute, string> valueFunc)
where TAttribute : Attribute
{
return typeof(TType).GetProperties()
.SelectMany(p => p.GetCustomAttributes())
.OfType<TAttribute>()
.ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), valueFunc);
}
Usage
var dictionary = GetAttribute<AuthorAttribute, Book>(a => a.Name);

public static class PropertyInfoExtensions
{
public static TValue GetAttributValue<TAttribute, TValue>(this PropertyInfo prop, Func<TAttribute, TValue> value) where TAttribute : Attribute
{
var att = prop.GetCustomAttributes(
typeof(TAttribute), true
).FirstOrDefault() as TAttribute;
if (att != null)
{
return value(att);
}
return default(TValue);
}
}
Usage:
//get class properties with attribute [AuthorAttribute]
var props = typeof(Book).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(AuthorAttribute)));
foreach (var prop in props)
{
string value = prop.GetAttributValue((AuthorAttribute a) => a.Name);
}
or:
//get class properties with attribute [AuthorAttribute]
var props = typeof(Book).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(AuthorAttribute)));
IList<string> values = props.Select(prop => prop.GetAttributValue((AuthorAttribute a) => a.Name)).Where(attr => attr != null).ToList();

While the above most upvoted answers definitely work, I'd suggest using a slightly different approach in some cases.
If your class has multiple properties with always the same attribute and you want to get those attributes sorted into a dictionary, here is how:
var dict = typeof(Book).GetProperties().ToDictionary(p => p.Name, p => p.GetCustomAttributes(typeof(AuthorName), false).Select(a => (AuthorName)a).FirstOrDefault());
This still uses cast but ensures that the cast will always work as you will only get the custom attributes of the type "AuthorName".
If you had multiple Attributes above answers would get a cast exception.

Here are some static methods you can use to get the MaxLength, or any other attribute.
using System;
using System.Linq;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;
public static class AttributeHelpers {
public static Int32 GetMaxLength<T>(Expression<Func<T,string>> propertyExpression) {
return GetPropertyAttributeValue<T,string,MaxLengthAttribute,Int32>(propertyExpression,attr => attr.Length);
}
//Optional Extension method
public static Int32 GetMaxLength<T>(this T instance,Expression<Func<T,string>> propertyExpression) {
return GetMaxLength<T>(propertyExpression);
}
//Required generic method to get any property attribute from any class
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(Expression<Func<T,TOut>> propertyExpression,Func<TAttribute,TValue> valueSelector) where TAttribute : Attribute {
var expression = (MemberExpression)propertyExpression.Body;
var propertyInfo = (PropertyInfo)expression.Member;
var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute),true).FirstOrDefault() as TAttribute;
if (attr==null) {
throw new MissingMemberException(typeof(T).Name+"."+propertyInfo.Name,typeof(TAttribute).Name);
}
return valueSelector(attr);
}
}
Using the static method...
var length = AttributeHelpers.GetMaxLength<Player>(x => x.PlayerName);
Or using the optional extension method on an instance...
var player = new Player();
var length = player.GetMaxLength(x => x.PlayerName);
Or using the full static method for any other attribute (StringLength for example)...
var length = AttributeHelpers.GetPropertyAttributeValue<Player,string,StringLengthAttribute,Int32>(prop => prop.PlayerName,attr => attr.MaximumLength);
Inspired by the Mikael Engver's answer.

I wrote this into a dynamic method since I use lots of attributes throughout my application. Method:
public static dynamic GetAttribute(Type objectType, string propertyName, Type attrType)
{
//get the property
var property = objectType.GetProperty(propertyName);
//check for object relation
return property.GetCustomAttributes().FirstOrDefault(x => x.GetType() == attrType);
}
Usage:
var objectRelAttr = GetAttribute(typeof(Person), "Country", typeof(ObjectRelationAttribute));
var displayNameAttr = GetAttribute(typeof(Product), "Category", typeof(DisplayNameAttribute));
Hope this helps anyone

Necromancing.
For those that still have to maintain .NET 2.0, or those that want to do it without LINQ:
public static object GetAttribute(System.Reflection.MemberInfo mi, System.Type t)
{
object[] objs = mi.GetCustomAttributes(t, true);
if (objs == null || objs.Length < 1)
return null;
return objs[0];
}
public static T GetAttribute<T>(System.Reflection.MemberInfo mi)
{
return (T)GetAttribute(mi, typeof(T));
}
public delegate TResult GetValue_t<in T, out TResult>(T arg1);
public static TValue GetAttributValue<TAttribute, TValue>(System.Reflection.MemberInfo mi, GetValue_t<TAttribute, TValue> value) where TAttribute : System.Attribute
{
TAttribute[] objAtts = (TAttribute[])mi.GetCustomAttributes(typeof(TAttribute), true);
TAttribute att = (objAtts == null || objAtts.Length < 1) ? default(TAttribute) : objAtts[0];
// TAttribute att = (TAttribute)GetAttribute(mi, typeof(TAttribute));
if (att != null)
{
return value(att);
}
return default(TValue);
}
Example usage:
System.Reflection.FieldInfo fi = t.GetField("PrintBackground");
wkHtmlOptionNameAttribute att = GetAttribute<wkHtmlOptionNameAttribute>(fi);
string name = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, delegate(wkHtmlOptionNameAttribute a){ return a.Name;});
or simply
string aname = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, a => a.Name );

Just looking for the right place to put this piece of code.
let's say you have the following property:
[Display(Name = "Solar Radiation (Average)", ShortName = "SolarRadiationAvg")]
public int SolarRadiationAvgSensorId { get; set; }
And you want to get the ShortName value. You can do:
((DisplayAttribute)(typeof(SensorsModel).GetProperty(SolarRadiationAvgSensorId).GetCustomAttribute(typeof(DisplayAttribute)))).ShortName;
Or to make it general:
internal static string GetPropertyAttributeShortName(string propertyName)
{
return ((DisplayAttribute)(typeof(SensorsModel).GetProperty(propertyName).GetCustomAttribute(typeof(DisplayAttribute)))).ShortName;
}

foreach (var p in model.GetType().GetProperties())
{
var valueOfDisplay =
p.GetCustomAttributesData()
.Any(a => a.AttributeType.Name == "DisplayNameAttribute") ?
p.GetCustomAttribute<DisplayNameAttribute>().DisplayName :
p.Name;
}
In this example I used DisplayName instead of Author because it has a field named 'DisplayName' to be shown with a value.

to get attribute from enum, i'm using :
public enum ExceptionCodes
{
[ExceptionCode(1000)]
InternalError,
}
public static (int code, string message) Translate(ExceptionCodes code)
{
return code.GetType()
.GetField(Enum.GetName(typeof(ExceptionCodes), code))
.GetCustomAttributes(false).Where((attr) =>
{
return (attr is ExceptionCodeAttribute);
}).Select(customAttr =>
{
var attr = (customAttr as ExceptionCodeAttribute);
return (attr.Code, attr.FriendlyMessage);
}).FirstOrDefault();
}
// Using
var _message = Translate(code);

If you want get property having the custom Attribute then please try the following:
IEnumerable propertyInfos = properties.GetType().GetProperties();
PropertyInfo p = propertyInfos.Where(x => x.GetCustomAttribute() != null);

Develop Reference

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.

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Reflection - get attribute name and value on property

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