Is there a way to know if all the properties in an object are empty. My object represents fields from database and I want to know if a particular record is present or not. NULL doesnt seem to work.
Have you tried checking against DBNull.Value
You can use reflection:
public static bool IsEmptyEntity<T>(T obj)
{
foreach (var property in typeof(T).GetProperties())
if (property.GetValue(obj, null) != null)
return false;
return true;
}
Usage:
public class MyTestEntity
{
public string Str { get; set; }
public int? Int { get; set; }
}
MyTestEntity test = new MyTestEntity();
var empty = IsEmptyEntity(test); //returns true
If the record is not present, then why would you have an object to represent it?
If your object represents fields from database, then it's probably a collection. If so, you can most likely use an extension method like myCollection.Any() to see if there are any objects inside the collection. Is that what you are asking for?
A lot of languages use a method or property called IsEmpty for this kind of check. During the hydration phase of the object set a boolean flag that specifies if the object is empty or not. Then you can simply use the property or method elsewhere to check for empty objects.
ie
During hydration
bool _isEmpty = false;
if( prop1 is empty && prop2 is empty )
{
_isEmpty = true;
}
else
{
_isEmpty = false;
}
Then use an IsEmpty property
IsEmpty
{
get { return _isEmpty; }
}
I've found occasions where using just a check with DBNull isn't enough. Maybe not the purest approach but a temporary check as a string seems to do the trick. Like so:
if ((DBNull.Value != field) &&
(!string.IsNullOrWhiteSpace(field.ToString())))
Related
Let's say I have a model class that looks like this:
public class ModelTest {
public string val1 {get;set;}
public string val2 {get;set;}
public string val3 {get;set;}
}
Somewhere in my code this ModelTest gets its data. The caveat is that, only 1 of them will hold a value
var model = new ModelTest() {val1=null, val2="value", val3=null} //Sudo code
What I am trying to do somehow, is compare a value to whichever 1 of the 3 items can potentially have a values, so something like:
var testCompare = "someValue"
if (testCompare == model. ....//how can I get the NOT NULL value from ModelTest here for comparison
While your data model isn't ideal, it is possible to check each of the properties by utilizing the || operator to compare each value. As long as your testCompare variable does not contain null, you can also omit a null check.
if (model.val1 == testCompare ||
model.val2 == testCompare ||
model.val3 == testCompare)
{ }
As mentioned in the comments, if you want a more succinct version, you can use the null coalescing operator, ??, to check subsequent properties if your prior property returns null. At the end of the null coalescing chain, the first non-null property will be compared to your testCompare string. Note that you must wrap all three properties in parentheses and that this has different behavior; it only tests the first non-null property whereas the previous version tests ALL properties for a match.
if (testCompare == (model.val1 ?? model.val2 ?? model.val3))
{
}
You could add a property to your ModelTest class that provides the first non-null value (if any) in your object:
public class ModelTest
{
public string val1 { get; set; }
public string val2 { get; set; }
public string val3 { get; set; }
public string val => val1 ?? val2 ?? val3;
}
and then check against that:
if (model.val == testCompare) { }
You could probably create a method (or even property) like:
public string Val()
{
if (val1 != null) return val1;
if (val2 != null) return val2;
if (val3 != null) return val3;
return null;
}
There is probably a shorter way to write this code. Also, if two or more of the values are not null, then it will return the first one.
It's a very bizarre use case, but let's go with it. Here's another option for the bonfire..
public class ModelTest {
private string _val;
public string val1 {get => _val; set => _val ??= value;}
public string val2 {get => _val; set => _val ??= value;}
public string val3 {get => _val; set => _val ??= value;}
}
Whichever one of these is set to non null ends up committing that value to _val - ??= writes the right hand into the left hand only if the left hand is null, essentially like left = left ?? right.
It doesn't matter which you use to access the value..
Note that there is only one data storage location so this approach is incapable of remembering two values, or which value was the non null. You wouldn't use this for disparate properties like name, address and social security number because it could lead to bizarre effects elsewhere. This is for a very narrow use case of "there are three properties that are essentially the same thing, they cannot be collapsed to one, and I don't know which one will be set but i can treat them equivalent for reading"
You can override the method 'Equals' of ModelTest class however you like. Example:
public class ModelTest {
public string val1 {get;set;}
public string val2 {get;set;}
public string val3 {get;set;}
public override bool Equals(object obj)
{
if(!typeof(string).IsInstanceOfType(obj))
return base.Equals(obj);
string value = obj as string;
if (val1.Equals(value))
return true;
if (val2.Equals(value))
return true;
if (val3.Equals(value))
return true;
return false;
}
}
For to use the method:
if(model.Equals("yourValue"))
...
What about solution which contains combination of reflection and Linq,
Test Data
var model = new ModelTest() {val1=null, val2="value", val3=null} ;
Usage
var result =
model.GetType()
.GetProperties()
.FirstOrDefault(prop => prop.GetValue(model, null) != null);
Print result
Console.WriteLine(result.GetValue(model));
This is my first attempt with reflection, suggestions are most welcome
.Net fiddle
Note: This is just an alternate solution, less performant. If you are looking for elegant solution, then kindly try other solutions.
I have class with multiple properties;
public class Employee
{
public string TYPE { get; set; }
public int? SOURCE_ID { get; set; }
public string FIRST_NAME { get; set; }
public string LAST_NAME { get; set; }
public List<Department> departmentList { get; set; }
public List<Address> addressList { get; set; }
}
sometimes this object return me with value in any property say
Employee emp = new Employee();
emp.FIRST_NAME= 'abc';
remaining values are null. This is OK
But, How do I check when all values in properties of objects are null
like string.IsNullOrEmpty() for object ?
curretly I am checking like this;
if(emp.FIRST_NAME == null && emp.LAST_NAME == null && emp.TYPE == null && emp.departmentList == null ...)
EDIT
This answer has received some votes in the last time, so I decided to improve it a little, adding simple caching so that ArePropertiesNotNull does not retrieve the properties every time it is called, but rather only once for every type.
public static class PropertyCache<T>
{
private static readonly Lazy<IReadOnlyCollection<PropertyInfo>> publicPropertiesLazy
= new Lazy<IReadOnlyCollection<PropertyInfo>>(() => typeof(T).GetProperties());
public static IReadOnlyCollection<PropertyInfo> PublicProperties => PropertyCache<T>.publicPropertiesLazy.Value;
}
public static class Extensions
{
public static bool ArePropertiesNotNull<T>(this T obj)
{
return PropertyCache<T>.PublicProperties.All(propertyInfo => propertyInfo.GetValue(obj) != null);
}
}
(Old answer below.)
You could use reflection as proposed by Joel Harkes, e.g. I put together this reusable, ready-to-use extension method
public static bool ArePropertiesNotNull<T>(this T obj)
{
return typeof(T).GetProperties().All(propertyInfo => propertyInfo.GetValue(obj) != null);
}
which can then be called like this
var employee = new Employee();
bool areAllPropertiesNotNull = employee.ArePropertiesNotNull();
And now you can check the areAllPropertiesNotNull flag which indicates whether all properties are not null. Returns true if all properties are not null, otherwise false.
Advantages of this approach
It doesn't matter whether or not the property type is nullable or not for the check.
Since above method is generic, you can use it for any type you want and don't have to write boilerplate code for every type you want to check.
It is more future-proof in case you change the class later. (noted by ispiro).
Disadvantages
Reflection can be quite slow, and in this case it is certainly slower than writing explicit code as you currently do. Using simple caching (as proposed by Reginald Blue will remove much of that overhead.
In my opinion, the slight performance overhead can be neglected since development time and repetition of code are reduced when using the ArePropertiesNotNull, but YMMV.
Either you do this by writing down the code to check every property manually (best option) or you use reflection (read more here)
Employee emp = new Employee();
var props = emp.GetType().GetProperties())
foreach(var prop in props)
{
if(prop.GetValue(foo, null) != null) return false;
}
return true;
example from here
Note that int cannot be null! and its default value will be 0. thus its better to check prop == default(int) than == null
option 3
Another option is to implement INotifyPropertyChanged.
On a change set a boolean field value isDirty to true and than you only need to check if this value is true to know if any property has been set (even if property was set with null.
Warning: this method every property can still be null but only checks if a setter was called (changing a value).
I have a class like this :
public class Test
{
public string STR1{ get; set; }
public INT INT1{ get; set; }
public DOUBLE DBL1{ get; set; }
public DATETIME DT1{ get; set; }
}
Normally, before saving the object, i will have to check all the properties inside this Class, and return a warning message if there is any empty/null property. There is easy way to do this by simply check each property like this :
if (string.IsNullOrEmpty(t.STR1))
return "STR1 is empty"
if (t.INT1 == 0)
return "INT1 = 0";
if (t.DBL1 == 0)
return "DBL1 = 0";
if (t.DT1 == DateTime.MinValue)
return "DT1 is empty"
But what if my class has more properties, actually it contains about 42 properties now, and still growing up. So i was thinking for a "cleaner" way to perform this check, and i found this topic which is quiet similar to my issue : Reflection (?) - Check for null or empty for each property/field in a class?
But this solution does not meet my need as i have to list the values that = null/empty string/0/DateTime.MinValue
Believe me, i wanted to post my "tried code" but i can't figure out a sensible LINQ query for this task (i'm a novice in C#)
Any help is greatly appreciated !
Since you need to test objects of different types, you can combine the solution from the linked question with use of dynamic to dispatch to the proper method.
First, define an overloaded method for each type.
private static IsEmpty(string s) { return string.IsNullOrEmpty(s); }
private static IsEmpty(double f) { return f == 0.0; }
private static IsEmpty(int i) { return i == 0; }
private static IsEmpty(DateTime d) { return d == DateTime.MinValue; }
Now you can use these methods in your check:
List<string> emptyProperties = typeof(MyType).GetProperties()
.Select(prop => new { Prop = prop, Val = prop.GetValue(obj, null) } )
.Where(val => IsEmpty((dynamic)val.Val) // <<== The "magic" is here
.Select(val => val.Prop.Name)
.ToList();
The tricky part of the code casts the value to dynamic, and then tells the runtime to find the most appropriate IsEmpty method for it. The downside to this approach is that the compiler has no way of telling whether the method is going to be found or not, so you may get exceptions at runtime for properties of unexpected type.
You can prevent these failures by adding a catch-all method taking object, like this:
private static IsEmpty(object o) { return o == null; }
I have a User object with a bunch of properties. I have a requirement that states when a user sets up their information, they need the ability to state which properties of their profile are visible to others.
The way I had envisioned this was adding an additional property - a list of string that would contain the property names that were publicly visible. I could then implement a method called ToPublicView() or something similar that would use reflection to set non-public properties to null or default.
Is this a reasonable approach, or is there a better way?
I think it's the simplest of the options. If reflection start to kill your performance, you may want to have a dictionary of property-delegate for accessing the values.
And as the requirement is not to have dynamic properties but just to mark the existing ones, it doesn't make sense to have all the properties in a dynamic way (like a list of property objects). Also, having them as actual properties will make the code more readable when you have to use it for the rest of the application.
In such a situation, if possible, I would suggest simply having a list of your properties, such as:
public Class Property<T>
{
public Property(string name, bool visible, T value)
{
Name = name;
Visible = visible;
Value = value;
}
string Name { get; set; }
bool Visible { get; set; }
T Value { get; set; }
}
Then you could create a list of the properties like this:
List<Property> properties = new List<Property>();
properties.Add(new Property<string>("FirstName", true, "Steve"));
If you need to be able to set the visibility today, you may need to set other meta-properties as well tomorrow. Color? Required/Optional? Size? Etc. Having your own Property type allows you to easily expand it in the future.
What? No. If that's the demand, then User properties should not be realized with actual properties, but instead using some sort of IEnumerable and Property objects, where each Property has its visibility, etc.
Can use, may be, some combination of custom DynamicObject implementation
EDIT
//custom property class
public class MyProperty
{
public bool IsVisible { get; set; }
public string PropertyName { get; set; }
}
public class Dymo: DynamicObject
{
Dictionary<MyProperty, object> dictionary
= new Dictionary<MyProperty, object>();
public override bool TryGetMember(
GetMemberBinder binder, out object result)
{
result = false;
var prop = PropertyFromName(binder.Name);
if (prop != null && prop.IsVisible)
return dictionary.TryGetValue(prop, out result);
return false;
}
public override bool TrySetMember(
SetMemberBinder binder, object value)
{
var prop = PropertyFromName(binder.Name);
if (prop != null && prop.IsVisible)
dictionary[prop] = value;
else
dictionary[new MyProperty { IsVisible = true, PropertyName = binder.Name}] = value;
return true;
}
private MyProperty PropertyFromName(string name)
{
return (from key in dictionary.Keys where key.PropertyName.Equals(name) select key).SingleOrDefault<MyProperty>();
}
public void SetPropertyVisibility(string propertyName, bool visibility)
{
var prop = PropertyFromName(propertyName);
if (prop != null)
prop.IsVisible = visibility;
}
}
and use this, after like this.
dynamic dynObj = new Dymo();
dynObj.Cartoon= "Mickey" ;
dynObj.SetPropertyVisibility("Mickey", false); //MAKE A PROPERTY "INVISIBLE"
What is the easiest way to take an objects and convert any of its values from null to string.empty ?
I was thinking about a routine that I can pass in any object, but I am not sure how to loop through all the values.
When your object exposes it's values via properties you can write something like:
string Value { get { return m_Value ?? string.Empty; } }
Another solution is to use reflection. This code will check properties of type string:
var myObject = new MyObject();
foreach( var propertyInfo in myObject.GetType().GetProperties() )
{
if(propertyInfo.PropertyType == typeof(string))
{
if( propertyInfo.GetValue( myObject, null ) == null )
{
propertyInfo.SetValue( myObject, string.Empty, null );
}
}
}
Using reflection, you could something similar to :
public static class Extensions
{
public static void Awesome<T>(this T myObject) where T : class
{
PropertyInfo[] properties = typeof(T).GetProperties();
foreach(var info in properties)
{
// if a string and null, set to String.Empty
if(info.PropertyType == typeof(string) &&
info.GetValue(myObject, null) == null)
{
info.SetValue(myObject, String.Empty, null);
}
}
}
}
Presumably, you have a report or a form somewhere showing "null" all over the place, instead of a nice, pleasant "".
It's best to leave the nulls as they are, and modify your display code wherever appropriate. Thus, a line like this:
label1.Text = someObject.ToString();
should become:
if (someObject == null)
{
label1.Text = ""; // or String.Empty, if you're one of *those* people
}
else
{
label1.Text = someObject.ToString();
}
and you can functionalize it as necessary:
public void DisplayObject(Label label, Object someObject)
{
if (someObject == null)
{
label.Text = ""; // or String.Empty, if you're one of *those* people
}
else
{
label.Text = someObject.ToString();
}
}
You could use reflection. Here's an example with one level of nesting:
class Foo
{
public string Prop1 { get; set; }
public string Prop2 { get; set; }
public string Prop3 { get; set; }
}
class Program
{
static void Main(string[] args)
{
var foo = new Foo
{
Prop1 = (string)null,
Prop2 = (string)null,
Prop3 = (string)null,
};
var props = typeof(Foo).GetProperties()
.Where(x => x.PropertyType == typeof(string));
foreach (var p in props)
{
p.SetValue(foo, string.Empty, null);
}
}
}
You can do that via reflection without too much trouble, and I am sure that by the time I post this there will be answers that tell you exactly how to do that.
But I personally don't like the reflection option.
I prefer to maintain object invariants for all of the object's members through a variety of means. For string members, the invariant is often that it not be null, and sometimes there are maximum length requirements as well (for storage in a database, for example). Other members have other sorts of invariants.
The first step is to create a method that checks all the invariants that you define for the object.
[Conditional("DEBUG")]
private void CheckObjectInvariant()
{
Debug.Assert(name != null);
Debug.Assert(name.Length <= nameMaxLength);
...
}
Then you call this after any method that manipulates the object in any way. Since it is decorated with the ConditionalAttribute, none of these calls will appear in the release version of the application.
Then you just have to make sure that none of the code allows any violations of these invariants. This means that the string fields need to have either initializers in their declarations or they need to be set in all the constructors for the object.
A special problem, and the one that probably motivated this question, is what to do about automatic properties.
public string Name { get; set; }
Obviously, this can be set to null at any time, and there's nothing you can do about that.
There are two options with regard to automatic properties. First, you can just not use them at all. This avoids the problem entirely. Second, you can just allow any possible string value. That is, any code that uses that property has to expect nulls, 10 mb strings or anything in between.
Even if you go with the reflection option to remove nulls, you still have to know when to call the magic-null-removal method on the object to avoid NullReferenceExceptions, so you haven't really bought anything that way.
+1 to Tanascius's answer. I used this answer but tweaked it a bit.
First I only grab the properties that are strings, so it doesn't loop through all my properties. Secondly, I placed in it my BaseEntity class that all my entities inherit from, which makes it global, so I don't have to put it on all my Entities.
public class BaseEntity
{
public int Id { get; set; }
public BaseEntity()
{
var stringProperties = this.GetType().GetProperties().Where(x => x.PropertyType == typeof(string));
foreach (var property in stringProperties)
{
if (property.GetValue(this, null) == null)
{
property.SetValue(this, string.Empty, null);
}
}
}
}