Links
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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
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Boolean operations
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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());
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Filter operation
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Expression<Func<IEnumerable<int>, IEnumerable<int>>> e1 = l => l.Select(x => x + 1);
Expression<Func<IEnumerable<int>, IEnumerable<int>>> e10 = l => l.Select(x => x + 10);
Expression<Func<IEnumerable<int>, IEnumerable<int>>> combinedExpresions = x => e10.Invoke(e1.Invoke(x));
Console.WriteLine(combinedExpresions.Expand()); // x => (x.Select(x => x + 1).Select(x => x + 10))
var list = new[] { 1, 2, 3 };
var result = combinedExp.Invoke(list).ToList(); // 12, 13, 14
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Allow to dynamically construct a lambda expression tree.
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var predicate = PredicateBuilder.New<User>();
predicate = predicate.And(x => x.Name.StartsWith("U"));
predicate = predicate.And(x => x.Name.EndsWith("2"));
context.Users.Where(predicate);
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dotnet add package LinqKit.Microsoft.EntityFrameworkCore
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