LINQKit

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AsExpandable

Csharp.svg
Expression<Func<User, bool>> expression = x => x.Name.EndsWith("2");

context.Users.Where(expression); // works fine !

// as x.Users is not a IQueryable, Any cannot take an Expression but a Func
// so we need to use Compile to get Func from Expression
context.Groups.Where(x => x.Users.Where(expression.Compile())); // Entity Framework will throw an exception

// solution: use AsExpandable
context.Groups.AsExpandable().Where(x => x.Users.Any(expression.Compile()));
// Compile never actually runs; AsExpandable will strip out the call to Compile and substitute it with a correct expression tree

Combining Expressions

Csharp.svg
Expression<Func<User, bool>> e1 = x => x.Name.StartsWith("U");
Expression<Func<User, bool>> e2 = x => x.Name.EndsWith("2");

Expression<Func<User, bool>> e3 = x => e1.Invoke(x) && e2.Invoke(x);

Console.WriteLine(e3.Expand());  // x => (x.Name.StartsWith("U") AndAlso x.Name.EndsWith("2"))

context.Users.Where(e3.Expand());

PredicateBuilder

Allow to dynamically construct a lambda expression tree.

Csharp.svg
var predicate = PredicateBuilder.New<User>(true);
predicate = predicate.And(x => x.Name.StartsWith("U"));
predicate = predicate.And(x => x.Name.EndsWith("2"));

context.Users.Where(predicate);

Installation

Bash.svg
dotnet add package LinqKit.Microsoft.EntityFrameworkCore