How to Create an Expression Tree Calling Ienumerable<Tsource>.Any(...)

How do I create an expression tree calling IEnumerableTSource.Any(...)?

There are several things wrong with how you're going about it.

1. You're mixing abstraction levels. The T parameter to GetAnyExpression<T> could be different to the type parameter used to instantiate propertyExp.Type. The T type parameter is one step closer in the abstraction stack to compile time - unless you're calling GetAnyExpression<T> via reflection, it will be determined at compile time - but the type embedded in the expression passed as propertyExp is determined at runtime. Your passing of the predicate as an Expression is also an abstraction mixup - which is the next point.

2. The predicate you are passing to GetAnyExpression should be a delegate value, not an Expression of any kind, since you're trying to call Enumerable.Any<T>. If you were trying to call an expression-tree version of Any, then you ought to pass a LambdaExpression instead, which you would be quoting, and is one of the rare cases where you might be justified in passing a more specific type than Expression, which leads me to my next point.

3. In general, you should pass around Expression values. When working with expression trees in general - and this applies across all kinds of compilers, not just LINQ and its friends - you should do so in a way that's agnostic as to the immediate composition of the node tree you're working with. You are presuming that you're calling Any on a MemberExpression, but you don't actually need to know that you're dealing with a MemberExpression, just an Expression of type some instantiation of IEnumerable<>. This is a common mistake for people not familiar with the basics of compiler ASTs. Frans Bouma repeatedly made the same mistake when he first started working with expression trees - thinking in special cases. Think generally. You'll save yourself a lot of hassle in the medium and longer term.

4. And here comes the meat of your problem (though the second and probably first issues would have bit you if you had gotten past it) - you need to find the appropriate generic overload of the Any method, and then instantiate it with the correct type. Reflection doesn't provide you with an easy out here; you need to iterate through and find an appropriate version.

So, breaking it down: you need to find a generic method (Any). Here's a utility function that does that:

static MethodBase GetGenericMethod(Type type, string name, Type[] typeArgs, 
    Type[] argTypes, BindingFlags flags)
{
    int typeArity = typeArgs.Length;
    var methods = type.GetMethods()
        .Where(m => m.Name == name)
        .Where(m => m.GetGenericArguments().Length == typeArity)
        .Select(m => m.MakeGenericMethod(typeArgs));

    return Type.DefaultBinder.SelectMethod(flags, methods.ToArray(), argTypes, null);
}

However, it requires the type arguments and the correct argument types. Getting that from your propertyExp Expression isn't entirely trivial, because the Expression may be of a List<T> type, or some other type, but we need to find the IEnumerable<T> instantiation and get its type argument. I've encapsulated that into a couple of functions:

static bool IsIEnumerable(Type type)
{
    return type.IsGenericType
        && type.GetGenericTypeDefinition() == typeof(IEnumerable<>);
}

static Type GetIEnumerableImpl(Type type)
{
    // Get IEnumerable implementation. Either type is IEnumerable<T> for some T, 
    // or it implements IEnumerable<T> for some T. We need to find the interface.
    if (IsIEnumerable(type))
        return type;
    Type[] t = type.FindInterfaces((m, o) => IsIEnumerable(m), null);
    Debug.Assert(t.Length == 1);
    return t[0];
}

So, given any Type, we can now pull the IEnumerable<T> instantiation out of it - and assert if there isn't (exactly) one.

With that work out of the way, solving the real problem isn't too difficult. I've renamed your method to CallAny, and changed the parameter types as suggested:

static Expression CallAny(Expression collection, Delegate predicate)
{
    Type cType = GetIEnumerableImpl(collection.Type);
    collection = Expression.Convert(collection, cType);

    Type elemType = cType.GetGenericArguments()[0];
    Type predType = typeof(Func<,>).MakeGenericType(elemType, typeof(bool));

    // Enumerable.Any<T>(IEnumerable<T>, Func<T,bool>)
    MethodInfo anyMethod = (MethodInfo)
        GetGenericMethod(typeof(Enumerable), "Any", new[] { elemType }, 
            new[] { cType, predType }, BindingFlags.Static);

    return Expression.Call(
        anyMethod,
            collection,
            Expression.Constant(predicate));
}

Here's a Main() routine which uses all the above code and verifies that it works for a trivial case:

static void Main()
{
    // sample
    List<string> strings = new List<string> { "foo", "bar", "baz" };

    // Trivial predicate: x => x.StartsWith("b")
    ParameterExpression p = Expression.Parameter(typeof(string), "item");
    Delegate predicate = Expression.Lambda(
        Expression.Call(
            p,
            typeof(string).GetMethod("StartsWith", new[] { typeof(string) }),
            Expression.Constant("b")),
        p).Compile();

    Expression anyCall = CallAny(
        Expression.Constant(strings),
        predicate);

    // now test it.
    Func<bool> a = (Func<bool>) Expression.Lambda(anyCall).Compile();
    Console.WriteLine("Found? {0}", a());
    Console.ReadLine();
}

How to express All have Any with Expression Trees

t was thought it would work as the Enumerable.All<TSource, Func<TSource, bool>> should be satisfied by the searchTagsConstant and anyCall

Nope. anyCall is not lambda expression (Func<TSource, bool>), only a potential body of such expression.

Let start from your target:

IEnumerable<long> searchTags = new List<long>() { 1, 2, 3 };

Expression<Func<Taggable, bool>> lambda = 
    taggable => searchTags.All(searchTag => taggable.Tags.Any(tag => tag.TagId == searchTag));

The easiest way to learn how to build expression tree is to create a sample expression at compile time and examine the generated code via some decompiler or the expression tree at runtime via debugger.

Anyway, note that the above expression has 3 lambda parameters, while in your attempt you have only 2. Also there is no Contains call, not sure why you've put in there.

Building the above expression can be like this:

var taggable = Expression.Parameter(typeof(Taggable), "taggable");
var tag = Expression.Parameter(typeof(Tag), "tag");
var searchTag = Expression.Parameter(typeof(long), "searchTag");
// tag.TagId == searchTag
var anyCondition = Expression.Equal(
    Expression.Property(tag, "TagId"),
    searchTag);
// taggable.Tags.Any(tag => tag.TagId == searchTag)
var anyCall = Expression.Call(
    typeof(Enumerable), nameof(Enumerable.Any), new[] { typeof(Tag) },
    Expression.Property(taggable, "Tags"), Expression.Lambda(anyCondition, tag));
// searchTags.All(searchTag => taggable.Tags.Any(tag => tag.TagId == searchTag))
var allCall = Expression.Call(
    typeof(Enumerable), nameof(Enumerable.All), new[] { typeof(long) },
    Expression.Constant(searchTags), Expression.Lambda(anyCall, searchTag));
// taggable => searchTags.All(searchTag => taggable.Tags.Any(tag => tag.TagId == searchTag))
var lambda = Expression.Lambda(allCall, taggable);

How to write an expression tree for selecting inside of SelectMany?

Unclear if you want it for IEnumerable or IQueryable... For IEnumerable:

Given:

/// <summary>
/// IEnumerable<TResult> Enumerable.SelectMany<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, IEnumerable<TResult>> selector)
/// </summary>
public static readonly MethodInfo SelectMany1 = (from x in typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public)
                                                    where x.Name == nameof(Enumerable.SelectMany)
                                                    let args = x.GetGenericArguments()
                                                    where args.Length == 2
                                                    let pars = x.GetParameters()
                                                    where pars.Length == 2 &&
                                                        pars[0].ParameterType == typeof(IEnumerable<>).MakeGenericType(args[0]) &&
                                                        pars[1].ParameterType == typeof(Func<,>).MakeGenericType(args[0], typeof(IEnumerable<>).MakeGenericType(args[1]))
                                                    select x).Single();

/// <summary>
/// IEnumerable<TResult> Enumerable.Select<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> selector)
/// </summary>
public static readonly MethodInfo Select1 = (from x in typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public)
                                                where x.Name == nameof(Enumerable.Select)
                                                let args = x.GetGenericArguments()
                                                where args.Length == 2
                                                let pars = x.GetParameters()
                                                where pars.Length == 2 &&
                                                    pars[0].ParameterType == typeof(IEnumerable<>).MakeGenericType(args[0]) &&
                                                    pars[1].ParameterType == typeof(Func<,>).MakeGenericType(args[0], args[1])
                                                select x).Single();

(I have a gist full of these definitions)

You can

// SelectMany
var par1 = Expression.Parameter(typeof(Person));
var sub1 = Expression.Property(par1, nameof(Person.Addresses));
var lambda1 = Expression.Lambda<Func<Person, IEnumerable<Address>>>(sub1, par1);
var selectMany = Expression.Call(SelectMany1.MakeGenericMethod(typeof(Person), typeof(Address)), par0, lambda1);

// Select
var par2 = Expression.Parameter(typeof(Address));
var sub2 = Expression.Property(par2, nameof(Address.City));
var lambda2 = Expression.Lambda<Func<Address, string>>(sub2, par2);
var select = Expression.Call(Select1.MakeGenericMethod(typeof(Address), typeof(string)), selectMany, lambda2);

// persons => Select(SelectMany(persons))
var par0 = Expression.Parameter(typeof(IEnumerable<>).MakeGenericType(typeof(Person)));
var lambda0 = Expression.Lambda<Func<IEnumerable<Person>, IEnumerable<string>>>(select, par0);
var compiled = lambda0.Compile();

If you want the SelectMany+Select call it is in the select variable. If you want a compilable expression that uses the SelectMany+Select, it is in lambda0 and in compiled.

Building a EF Compatible expression call using Any against any type

Use the following extension method:

public static class QueryableExtensions
{
    public static IQueryable<T> AnyFromItems<T>(this IQueryable<T> source, string items, string propName)
    {
        var strItems = items.Split(",", StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);

        var entityParam = Expression.Parameter(typeof(T), "e");
        var propExpression = Expression.PropertyOrField(entityParam, propName);
        var itemType = propExpression.Type;
        var itemParam = Expression.Parameter(itemType, "i");

        var anyPredicate =
            Expression.Lambda(
                Expression.Equal(itemParam, propExpression),
                itemParam);

        // apply conversion
        var itemsExpression = Expression.Call(typeof(QueryableExtensions), nameof(QueryableExtensions.ParseItems),
            new[] { itemType }, Expression.Constant(strItems));

        var filterLambda =
            Expression.Lambda<Func<T, bool>>(
                Expression.Call(typeof(Enumerable), nameof(Enumerable.Any), new[] { itemType },
                    itemsExpression, anyPredicate),
                entityParam);

        return source.Where(filterLambda);
    }

    private static IEnumerable<TItem> ParseItems<TItem>(IEnumerable<string> items)
    {
        return items.Select(i => (TItem)Convert.ChangeType(i, typeof(TItem)));
    }
}

And usage:

var query = new Query
{
    PropertyName = "id",
    AnyValues = string.Join(", ", new List<Guid> { Guid.Empty });
};

var people = await context.DbSet<Person>()
    .AnyFromItems(query.AnyValues, query.PropertyName)
    .ToListAsync();

Expression Tree for Enumerable.Select

You can simplify this problem by removing the dynamic type from the equation. You can reproduce the same issue with the code below, which does exactly the same thing, but without the dynamic type.

static class Program
{
    private static void Main(string[] args)
    {
        var list = new List<Pet>();
        var eList = Expression.Constant(list);
        var pe = Expression.Parameter(typeof(Pet), "p");
        var method = typeof(Program).GetMethod("CreateObject", BindingFlags.Static | BindingFlags.NonPublic);
        var properties = typeof(Pet).GetProperties().Where(pi => pi.Name == "Name"); //will be defined by user
        var selectorBody = Expression.Call(method, Expression.Constant(properties));
        var selector = Expression.Lambda(selectorBody, pe);
        var res = Expression.Call(typeof(Enumerable), "Select", new[] { typeof(Pet), CreateType(properties) }, eList, selector);
    }

    private static Type CreateType(IEnumerable<PropertyInfo> properties)
    {
        return typeof (DynamicType);
    }

    private static object CreateObject(IEnumerable<PropertyInfo> properties)
    {
        var type = CreateType(properties);
        return  Activator.CreateInstance(type);
    }

    class Pet
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    class DynamicType
    {
        public string Name { get; set; }
    }
}

So the problem is the method signature of CreateObject. Since its return type isn't the dynamic type, the lambda isn't valid. You can see this by changing the type of CreateObject.

    // this works fine
    private static DynamicType CreateObject(IEnumerable<PropertyInfo> properties)
    {
        var type = CreateType(properties);
        return  (DynamicType) Activator.CreateInstance(type);
    }

Since you're dealing with a dynamic type, you need to build an expression to cast the result of CreateObject to your dynamic type. Try using something like this:

        // create dynamic type
        var properties = typeof(Pet).GetProperties().Where(pi => pi.Name == "Name"); //will be defined by user
        var dynamicType = CreateType(properties);

        // build expression
        var list = new List<Pet>();
        var eList = Expression.Constant(list);
        var pe = Expression.Parameter(typeof(Pet), "p");
        var createObjectMethod = typeof(Program).GetMethod("CreateObject", BindingFlags.Static | BindingFlags.NonPublic);
        var createObjectCall = Expression.Call(createObjectMethod, Expression.Constant(properties));
        var castExpression = Expression.Convert(createObjectCall, dynamicType);
        var selectorExpression = Expression.Lambda(castExpression, pe);
        var res = Expression.Call(typeof(Enumerable), "Select", new[] { typeof(Pet), dynamicType }, eList, selectorExpression);

OrderBy Expression Tree in Net Core Linq for Extension Method

Check the sample code for the solution:

void Main()
{
    var queryableRecords = Product.FetchQueryableProducts();

    Expression expression = queryableRecords.OrderBy("Name");

    var func = Expression.Lambda<Func<IQueryable<Product>>>(expression)
                         .Compile();

    func().Dump();
}

public class Product
{
    public int Id { get; set; }

    public string Name { get; set; }

    public static IQueryable<Product> FetchQueryableProducts()
    {
        List<Product> productList = new List<Product>()
        {
          new Product {Id=1, Name = "A"},
          new Product {Id=1, Name = "B"},
          new Product {Id=1, Name = "A"},
          new Product {Id=2, Name = "C"},
          new Product {Id=2, Name = "B"},
          new Product {Id=2, Name = "C"},
        };

        return productList.AsQueryable();
    }
}

public static class ExpressionTreesExtesion
{

    public static Expression OrderBy(this IQueryable queryable, string propertyName)
    {
        var propInfo = queryable.ElementType.GetProperty(propertyName);

        var collectionType = queryable.ElementType;

        var parameterExpression = Expression.Parameter(collectionType, "g");
        var propertyAccess = Expression.MakeMemberAccess(parameterExpression, propInfo);
        var orderLambda = Expression.Lambda(propertyAccess, parameterExpression);
        return Expression.Call(typeof(Queryable),
                               "OrderBy",
                               new Type[] { collectionType, propInfo.PropertyType },
                               queryable.Expression,
                               Expression.Quote(orderLambda));

    }

}

Result

How it Works:

Created an expression using extension method on the Queryable type, which internally calls OrderBy method of the Queryable type, expecting IQueryable to be the Input, along with the field name and thus runs the ordering function and Ordered collection is the final Output

Option 2:

This may fit your use case better, here instead of calling OrderBy method, we are creating the Expression<Func<T,string>> as an extension method to the IEnumerable<T>, which can then be compiled and supplied to the OrderBy Call, as shown in the example and is thus much more intuitive and simple solution:

Creating Expression:

public static class ExpressionTreesExtesion
{
    public static Expression<Func<T,string>> OrderByExpression<T>(this IEnumerable<T> enumerable, string propertyName)
    {
        var propInfo = typeof(T).GetProperty(propertyName);

        var collectionType = typeof(T);

        var parameterExpression = Expression.Parameter(collectionType, "x");
        var propertyAccess = Expression.MakeMemberAccess(parameterExpression, propInfo);
        var orderExpression = Expression.Lambda<Func<T,string>>(propertyAccess, parameterExpression);
        return orderExpression;
    }
}

How to Call:

var ProductExpression = records.OrderByExpression("Name");

var result  = records.OrderBy(ProductExpression.Compile());

ProductExpression.Compile() above will compile into x => x.Name, where column name is supplied at the run-time

Please note in case the ordering field can be other types beside string data type, then make that also generic and supply it while calling extension method, only condition being property being called shall have the same type as supplied value, else it will be a run-time exception, while creating Expression

Edit 1, how to make the OrderType field also generic

public static Expression<Func<T, TField>> OrderByFunc<T,TField>(this IEnumerable<T> enumerable, string propertyName)
    {
        var propInfo = typeof(T).GetProperty(propertyName);

        var collectionType = typeof(T);

        var parameterExpression = Expression.Parameter(collectionType, "x");
        var propertyAccess = Expression.MakeMemberAccess(parameterExpression, propInfo);
        var orderExpression = Expression.Lambda<Func<T, TField>>(propertyAccess, parameterExpression);
        return orderExpression;
    }

How to call:

Now both the types need to be explicitly supplied, earlier were using generic type inference from IEnumerable<T>:

// For Integer Id field

var ProductExpression = records.OrderByFunc<Product,int>("Id");

// For string name field

var ProductExpression = records.OrderByFunc<Product,string>("Name");

Build IQueryable.Any with Expression Trees for LINQ queries

Calling an extension method, like Enumerable.Any or Queryable.Any, is simply a static method call on the sequence and the lambda expression you created for the WHERE clause. You can use Expression.Call to do this:

// for Enumerable.Any<T>(IEnumerable<T>,Predicate<T>)
var overload = typeof(Enumerable).GetMethods("Any")
                                 .Single(mi => mi.GetParameters().Count() == 2);
var call = Expression.Call(
    overload,
    Expression.PropertyOrField(projParam, "GroupsAssigned"),
    anyLambda);      

For Queryable.Any<T>, you'll need to roll this up into a method:

static Expression BuildAny<TSource>(Expression<Func<TSource, bool>> predicate)
{
    var overload = typeof(Queryable).GetMethods("Any")
                              .Single(mi => mi.GetParameters().Count() == 2);
    var call = Expression.Call(
        overload,
        Expression.PropertyOrField(projParam, "GroupsAssigned"),
        predicate);   

    return call;
}

Although this seems odd that you're unable to do this through a normal query.

---

Related Topics