I have a REST WebAPI using EntityFramework database first. All code is generated off the EDMX file, entities, repository classes and API controllers etc.
I have added some filtering functionality which allows users to add conditions via the query string that translate to LinqKit PredicateBuilder / Linq expressions that filter results when hitting the db.
e.g. /api/Users?FirstName_contains=Rog
This will return all users with 'Rog' in the User.FirstName member. This uses PredicateBuilder to dynamically build an appropriate Linq expression to then use as a Where clause against the DbSet.
For example:
var fieldName = "FirstName";
var value = "Rog";
var stringContainsMethod = typeof(string).GetMethod("Contains", new[] { typeof(string) });
var parameter = Expression.Parameter(typeof(User), "m");
var fieldAccess = Expression.PropertyOrField(parameter, fieldName);
var fieldType = typeof(User).GetProperty(fieldName, BindingFlags.IgnoreCase | BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Public).PropertyType;
var expression = Expression.Lambda<Func<User, bool>>(Expression.Call(fieldAccess, stringContainsMethod, Expression.Constant(value, fieldType))
, parameter)
var andPredicate = PredicateBuilder.True<User>();
andPredicate = andPredicate.And(expression);
var query = Db.Users
.AsQueryable()
.AsExpandable()
.Where(andPredicate);
Now the problem. I want the client to be able to match results based on a composition of members.
e.g. /api/Users?api_search[FirstName,LastName]=Rog
i.e. search first name + last name for matches of 'Rog', so I could search for 'Roger Sm' and get a result for first name = Roger and last name = Smith.
If I was to query the DbSet using fluent it would look like:
users.Where(u => (u.FirstName + " " + u.LastName).Contains("Rog"));
What I am struggling with is creating a predicate / linq expression that will handle the concatenation of string members FirstName + " " + LastName dynamically.
PredicateBuilder is not really needed here.
The string concatenation expression can be generated using string.Concat method call which is supported by EF:
static Expression<Func<T, string>> GenerateConcat<T>(IEnumerable<string> propertyNames)
{
var parameter = Expression.Parameter(typeof(T), "e");
// string.Concat(params string[] values)
var separator = Expression.Constant(" ");
var concatArgs = Expression.NewArrayInit(typeof(string), propertyNames
.SelectMany(name => new Expression[] { separator, Expression.PropertyOrField(parameter, name) })
.Skip(1));
var concatCall = Expression.Call(typeof(string).GetMethod("Concat", new[] { typeof(string[]) }), concatArgs);
return Expression.Lambda<Func<T, string>>(concatCall, parameter);
}
The string contains predicate can be generated by simple string.Contains method call:
static Expression<Func<T, bool>> GenerateContains<T>(Expression<Func<T, string>> member, string value)
{
var containsCall = Expression.Call(member.Body, "Contains", Type.EmptyTypes, Expression.Constant(value));
return Expression.Lambda<Func<T, bool>>(containsCall, member.Parameters);
}
Combining them together with your example:
var predicate = GenerateContains(GenerateConcat<User>(new[] { "FirstName", "LastName" }), "Rog");
Try the following (I haven't tested it against a database):
public class User
{
public string FirstName { get; set; }
public string LastName { get; set;}
}
void Main()
{
List<User> users = new List<User> {
new User { FirstName = "john", LastName = "smith" },
new User { FirstName = "siler", LastName = "johnston" } };
string searchName = "ja smi";
String[] terms = searchName.Split(' ');
var items = users.Where(x => terms.Any(y => x.FirstName.Contains(y))
|| terms.Any(y => x.LastName.Contains(y)));
}
Related
I try to perform a simple LIKE action on the database site, while having query building services based on generic types. I found out while debugging however, that performing EF.Functions.Like() with reflection does not work as expected:
The LINQ expression 'where __Functions_0.Like([c].GetType().GetProperty("FirstName").GetValue([c], null).ToString(), "%Test%")' could not be translated and will be evaluated locally..
The code that makes the difference
That works:
var query = _context.Set<Customer>().Where(c => EF.Functions.Like(c.FirstName, "%Test%"));
This throws the warning & tries to resolve in memory:
var query = _context.Set<Customer>().Where(c => EF.Functions.Like(c.GetType().GetProperty("FirstName").GetValue(c, null).ToString(), "%Test%"));
Does the Linq query builder or the EF.Functions not support reflections?
Sorry if the questions seem basic, it's my first attempt with .NET Core :)
In EF the lambdas are ExpressionTrees and the expressions are translated to T-SQL so that the query can be executed in the database.
You can create an extension method like so:
public static IQueryable<T> Search<T>(this IQueryable<T> source, string propertyName, string searchTerm)
{
if (string.IsNullOrEmpty(propertyName) || string.IsNullOrEmpty(searchTerm))
{
return source;
}
var property = typeof(T).GetProperty(propertyName);
if (property is null)
{
return source;
}
searchTerm = "%" + searchTerm + "%";
var itemParameter = Parameter(typeof(T), "item");
var functions = Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var like = typeof(DbFunctionsExtensions).GetMethod(nameof(DbFunctionsExtensions.Like), new Type[] { functions.Type, typeof(string), typeof(string) });
Expression expressionProperty = Property(itemParameter, property.Name);
if (property.PropertyType != typeof(string))
{
expressionProperty = Call(expressionProperty, typeof(object).GetMethod(nameof(object.ToString), new Type[0]));
}
var selector = Call(
null,
like,
functions,
expressionProperty,
Constant(searchTerm));
return source.Where(Lambda<Func<T, bool>>(selector, itemParameter));
}
And use it like so:
var query = _context.Set<Customer>().Search("FirstName", "Test").ToList();
var query2 = _context.Set<Customer>().Search("Age", "2").ToList();
For reference this was the Customer I used:
public class Customer
{
[Key]
public Guid Id { get; set; }
public string FirstName { get; set; }
public int Age { get; set; }
}
Simple answer, no.
EntityFramework is trying to covert your where clause in to a SQL Query. There is no native support for reflection in this conversation.
You have 2 options here. You can construct your text outside of your query or directly use property itself. Is there any specific reason for not using something like following?
var query = _context.Set<Customer>().Where(c => EF.Functions.Like(c.FirstName, "%Test%"));
Keep in mind that every ExpresionTree that you put in Where clause has to be translated into SQL query.
Because of that, ExpressionTrees that you can write are quite limited, you have to stick to some rules, thats why reflection is not supported.
Image that instead of :
var query = _context.Set<Customer>().Where(c => EF.Functions.Like(c.GetType().GetProperty("FirstName").GetValue(c, null).ToString(), "%Test%"));
You write something like:
var query = _context.Set<Customer>().Where(c => EF.Functions.Like(SomeMethodThatReturnsString(c), "%Test%"));
It would mean that EF is able to translate any c# code to SQL query - it's obviously not true :)
I chucked together a version of the accepted answer for those using NpgSQL as their EF Core provider as you will need to use the ILike function instead if you want case-insensitivity, also added a second version which combines a bunch of properties into a single Where() clause:
public static IQueryable<T> WhereLike<T>(this IQueryable<T> source, string propertyName, string searchTerm)
{
// Check property name
if (string.IsNullOrEmpty(propertyName))
{
throw new ArgumentNullException(nameof(propertyName));
}
// Check the search term
if(string.IsNullOrEmpty(searchTerm))
{
throw new ArgumentNullException(nameof(searchTerm));
}
// Check the property exists
var property = typeof(T).GetProperty(propertyName);
if (property == null)
{
throw new ArgumentException($"The property {typeof(T)}.{propertyName} was not found.", nameof(propertyName));
}
// Check the property type
if(property.PropertyType != typeof(string))
{
throw new ArgumentException($"The specified property must be of type {typeof(string)}.", nameof(propertyName));
}
// Get expression constants
var searchPattern = "%" + searchTerm + "%";
var itemParameter = Expression.Parameter(typeof(T), "item");
var functions = Expression.Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var likeFunction = typeof(NpgsqlDbFunctionsExtensions).GetMethod(nameof(NpgsqlDbFunctionsExtensions.ILike), new Type[] { functions.Type, typeof(string), typeof(string) });
// Build the property expression and return it
Expression selectorExpression = Expression.Property(itemParameter, property.Name);
selectorExpression = Expression.Call(null, likeFunction, functions, selectorExpression, Expression.Constant(searchPattern));
return source.Where(Expression.Lambda<Func<T, bool>>(selectorExpression, itemParameter));
}
public static IQueryable<T> WhereLike<T>(this IQueryable<T> source, IEnumerable<string> propertyNames, string searchTerm)
{
// Check property name
if (!(propertyNames?.Any() ?? false))
{
throw new ArgumentNullException(nameof(propertyNames));
}
// Check the search term
if (string.IsNullOrEmpty(searchTerm))
{
throw new ArgumentNullException(nameof(searchTerm));
}
// Check the property exists
var properties = propertyNames.Select(p => typeof(T).GetProperty(p)).AsEnumerable();
if (properties.Any(p => p == null))
{
throw new ArgumentException($"One or more specified properties was not found on type {typeof(T)}: {string.Join(",", properties.Where(p => p == null).Select((p, i) => propertyNames.ElementAt(i)))}.", nameof(propertyNames));
}
// Check the property type
if (properties.Any(p => p.PropertyType != typeof(string)))
{
throw new ArgumentException($"The specified properties must be of type {typeof(string)}: {string.Join(",", properties.Where(p => p.PropertyType != typeof(string)).Select(p => p.Name))}.", nameof(propertyNames));
}
// Get the expression constants
var searchPattern = "%" + searchTerm + "%";
var itemParameter = Expression.Parameter(typeof(T), "item");
var functions = Expression.Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var likeFunction = typeof(NpgsqlDbFunctionsExtensions).GetMethod(nameof(NpgsqlDbFunctionsExtensions.ILike), new Type[] { functions.Type, typeof(string), typeof(string) });
// Build the expression and return it
Expression selectorExpression = null;
foreach (var property in properties)
{
var previousSelectorExpression = selectorExpression;
selectorExpression = Expression.Property(itemParameter, property.Name);
selectorExpression = Expression.Call(null, likeFunction, functions, selectorExpression, Expression.Constant(searchPattern));
if(previousSelectorExpression != null)
{
selectorExpression = Expression.Or(previousSelectorExpression, selectorExpression);
}
}
return source.Where(Expression.Lambda<Func<T, bool>>(selectorExpression, itemParameter));
}
I have a situation where I am using a linq provider that does not support the .Contains method to generate a WHERE IN clause in the query. I am looking for a way to generate the (Value = X OR Value = Y OR Value = Z) statement dynamically from the list of items to match. I haven't found a good example of building expression trees to do this.
Normally I would query this way:
var names = new string[] { "name1", "name2", "name3" }
var matches = query.Where(x => names.Contains(x.Name));
So far the closest thing I could find was to use the
Dynamic Linq Library and build a string to be interpreted but it feels a bit too hacky.
You don't even need an external library for something like this:
var names = new string[] { "name1", "name2", "name3" };
// Where MyClass is the type of your class
ParameterExpression par = Expression.Parameter(typeof(MyClass));
MemberExpression prop = Expression.Property(par, "Name");
Expression expression = null;
foreach (string name in names)
{
Expression expression2 = Expression.Equal(prop, Expression.Constant(name));
if (expression == null)
{
expression = expression2;
}
else
{
expression = Expression.OrElse(expression, expression2);
}
}
var query = ...; // Your query
if (expression != null)
{
// Where MyClass is the type of your class
var lambda = Expression.Lambda<Func<MyClass, bool>>(expression, par);
query = query.Where(lambda);
}
You can build a concatenation of Expression.OrElse, with the comparisons between the property Name and one of the strings.
In this particular case (3 strings), the resulting Expression, when looked from the debugger, is:
(((Param_0.Name == "name1") OrElse (Param_0.Name == "name2")) OrElse (Param_0.Name == "name3"))
Just improving the answer by xanatos:
var names = new string[] { "name1", "name2", "name3" };
var query = ...; // Your query
if (names.Any())
{
// Where MyClass is the type of your class
ParameterExpression par = Expression.Parameter(typeof(MyClass));
MemberExpression prop = Expression.Property(par, "Name");
var expression=names
.Select(v => Expression.Equal(prop, Expression.Constant(v)))
.Aggregate(Expression.OrElse);
// Where MyClass is the type of your class
var lambda = Expression.Lambda<Func<MyClass, bool>>(expression, par);
query = query.Where(lambda);
}
I have an MVC4 program in which I have a dropdown with a list of all of the properties of a model. I want the user to be able to select which property then type in a string value to the textbox to search. The issue is I can't dynamically change the query with the value of the dropdown.
public ActionResult SearchIndex(string searchString, string searchFields)
{
var selectListItems = new List<SelectListItem>();
var first = db.BloodStored.First();
foreach(var item in first.GetType().GetProperties())
{
selectListItems.Add(new SelectListItem(){ Text = item.Name, Value = item.Name});
}
IEnumerable<SelectListItem> enumSelectList = selectListItems;
ViewBag.SearchFields = enumSelectList;
var bloodSearch = from m in db.BloodStored
select m;
if (!String.IsNullOrEmpty(searchString))
{
PropertyInfo selectedSearchField = getType(searchFields);
string fieldName = selectedSearchField.Name;
//Dynamic Linq query this is how it needs to be set up to pass through linq.dynamic without exception
bloodSearch = bloodSearch.Where("x => x." + fieldName + " == " + "#0", searchString).OrderBy("x => x." + fieldName);
return View(bloodSearch);
}
return View(bloodSearch);
}
Here is my getType method
public PropertyInfo getType(string searchFields)
{
var first = db.BloodStored.First();
foreach (var item in first.GetType().GetProperties())
{
if(searchFields == item.Name)
{
return item;
}
}
return null;
}
I have updated my code to reflect the working query encase it can help anyone else out.
Here is a link to the post that I found my answer from Dynamic query with LINQ won't work
you should use the Dynamic.cs library. you can find it here as well as examples. You can then create your where clauses dynamically.
dynamic.cs
you could build the expression yourself.
static Expression<Func<T, bool>> GetExpression<T>(string propertyName, string propertyValue)
{
var parameterExp = Expression.Parameter(typeof(T), "type");
var propertyExp = Expression.Property(parameterExp, propertyName);
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
var someValue = Expression.Constant(propertyValue, typeof(string));
var containsMethodExp = Expression.Call(propertyExp, method, someValue);
return Expression.Lambda<Func<T, bool>>(containsMethodExp, parameterExp);
}
stole this from a post by Marc Gravell.
I'm trying to generate a LINQ OrderBy clause using lambda expressions with an input of the column name of an entity as a string (in the "sortOn" variable below).
The code below works fine for a sortOn value like "Code" generating the lambda
p => p.Code
But I would also like to sort on a child entity, where the lambda might be
p => p.Category.Description
So in this instance, I would just like to set sortOn = "Category.Description" and have the correct lamdba expression generated.
Is this possible? Any suggestions about the best way to do this would be welcomed.
This code works fine for the simple case:
var param = Expression.Parameter(typeof (Product), "p");
var sortExpression = Expression.Lambda<Func<Product, object>>(
Expression.Property(param, sortOn), param);
if (sortAscending ?? true)
{
products = products.OrderBy(sortExpression);
}
else
{
products = products.OrderByDescending(sortExpression);
}
The use-case for this problem is displaying a grid of data and being able to sort the data, simply by passing the column name to be sorted on back to the server. I'd like to make the solution generic, but have started using a particular type (Product in the example) for now.
This will generate proper lambda expression:
var sortOn = "Category.Description";
var param = Expression.Parameter(typeof(Product), "p");
var parts = sortOn.Split('.');
Expression parent = param;
foreach (var part in parts)
{
parent = Expression.Property(parent, part);
}
var sortExpression = Expression.Lambda<Func<Product, object>>(parent, param);
Here is an extension OrderBy method which works for any number of nested parameters.
public static IQueryable<T> OrderBy<T>(this IQueryable<T> query, string key, bool asc = true)
{
try
{
string orderMethodName = asc ? "OrderBy" : "OrderByDescending";
Type type = typeof(T);
Type propertyType = type.GetProperty(key)?.PropertyType; ;
var param = Expression.Parameter(type, "x");
Expression parent = param;
var keyParts = key.Split('.');
for (int i = 0; i < keyParts.Length; i++)
{
var keyPart = keyParts[i];
parent = Expression.Property(parent, keyPart);
if (keyParts.Length > 1)
{
if (i == 0)
{
propertyType = type.GetProperty(keyPart).PropertyType;
}
else
{
propertyType = propertyType.GetProperty(keyPart).PropertyType;
}
}
}
MethodCallExpression orderByExpression = Expression.Call(
typeof(Queryable),
orderMethodName,
new Type[] { type, propertyType },
query.Expression,
CreateExpression(type, key)
);
return query.Provider.CreateQuery<T>(orderByExpression);
}
catch (Exception e)
{
return query;
}
}
The CreateExpression method which is used in my solution is defined in this post.
The usage of the OrderBy extension method is as follows.
IQueryable<Foo> q = [Your database context].Foos.AsQueryable();
IQueryable<Foo> p = null;
p = q.OrderBy("myBar.name"); // Ascending sort
// Or
p = q.OrderBy("myBar.name", false); // Descending sort
// Materialize
var result = p.ToList();
The type Foo and its properties are also taken from the same post as method CreateExpression.
Hope you find this post helpful.
You can use the Dynamic LINQ Query Library to do this easily. Assuming you have an IQueryable<T> implementation of Product, you can easily do:
IQueryable<Product> products = ...;
// Order by dynamically.
products = products.OrderBy("Category.Description");
The blog post has a link to the libary, and you'll have to build/include the project in your solution yourself, but it works very well, and the parsing is very robust. It prevents you from having to write the parsing code yourself; even for something so simple, if the requirements expand, the library has you covered, whereas a homegrown solution does not.
It also has a number of other dynamic operators (Select, Where, etc.) so you can perform other dynamic operations.
There's no magic under the hood, it just parses the strings you pass it and then creates the lambda expressions based on the parsing results.
If you don't need expressions, how about:
products = products.Orderby(p1 => p1.Code).ThenBy(p2 => p2.Category.Description)
Hi you can also create an extension method like which can sort to any depth not only just child
public static IEnumerable<TSource> CustomOrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
List<string> list=new List<string>();
List<TSource> returnList=new List<TSource>();
List<int> indexList = new List<int>();
if (source == null)
return null;
if (source.Count() <= 0)
return source;
source.ToList().ForEach(sc=>list.Add(keySelector(sc).ToString())); //Extract the strings of property to be ordered
list.Sort(); //sort the list of strings
foreach (string l in list) // extract the list of indexes of source according to the order
{
int i=0;
//list.ForEach(l =>
foreach (var s in source.ToList())
{
if (keySelector(s).ToString() == l)
break;
i++;
}
indexList.Add(i);
}
indexList.ForEach(i=>returnList.Add(source.ElementAt(i))); //rearrange the source according to the above extracted indexes
return returnList;
}
}
public class Name
{
public string FName { get; set; }
public string LName { get; set; }
}
public class Category
{
public Name Name { get; set; }
}
public class SortChild
{
public void SortOn()
{
List<Category> category = new List<Category>{new Category(){Name=new Name(){FName="sahil",LName="chauhan"}},
new Category(){Name=new Name(){FName="pankaj",LName="chauhan"}},
new Category(){Name=new Name(){FName="harish",LName="thakur"}},
new Category(){Name=new Name(){FName="deepak",LName="bakseth"}},
new Category(){Name=new Name(){FName="manish",LName="dhamaka"}},
new Category(){Name=new Name(){FName="arev",LName="raghaka"}}
};
var a = category.CustomOrderBy(s => s.Name.FName);
}
}
Its custom method and right now it works only for string property only however it can be reactified using generics to work for any primitive type. I hope this will help.
I was trying to generate a simple Lambda Expression at runtime with no luck... something like this:
var result = queryableData.Where(item => item.Name == "Soap")
Here is my example class and a fixture queryable:
public class Item
{
public int Id { get; set; }
public string Name { get; set; }
}
IQueryable<Item> queryableData = ...;
Then I generate a lambda expression at runtime correct code follows:
//"item" in "item =>..."
var item = Expression
.Parameter(typeof(Item), "item");
//property of my item, this is "item.Name"
var prop = Expression
.Property(item, "Name");
//then "Soap" in '... => item.Name=="Soap"'
var value = Expression.Constant("Soap");
//equality expression "==" in my primer
var equals = Expression.Equal(prop, value);
//then lambda
var lambda = Expression.Lambda<Func<Item, bool>>(equals, item);
//and here are the results
var results = queryableData.Where(lambda);
Big thanks to dtb for advice!
In the following query
var result = query.Where(item => item.Name == "Soap")
the lambda expression is
item => item.Name == "Soap"
You only need to construct this part, not the Where call which accepts an expression tree.
The expression tree for the lambda expression looks like this:
Lambda
/ \
Equal Parameter
/ \ item
Property \
"Name" Constant
| "Soap"
Parameter
item
In code:
var item = Expression.Parameter(typeof(Item), "item");
var prop = Expression.Property(item, "Name");
var soap = Expression.Constant("Soap");
var equal = Expression.Equal(prop, soap);
var lambda = Expression.Lambda<Func<Item, bool>>(equal, item);
var result = queryableData.Where(lambda);