"The Linq Expression Node Type 'Invoke' Is Not Supported in Linq to Entities" - Stumped!

The LINQ expression node type 'Invoke' is not supported in LINQ to Entities - stumped!

You're trying to pass an arbitrary .NET function in... how could the entity framework hope to translate that into SQL? You can change it to take an Expression<Func<int, bool>> instead, and build the Where clause from that, although it won't be particularly easy, because you'll need to rewrite the expression with a different parameter expression (i.e. replacing whatever parameter expression is in the original expression tree with the expression of calling u.RelationTypeId).

To be honest, for the sake of just specifying u.RelationTypeId in the lambda expression that you use to create the expression tree to pass into the method, you'd be better off just using:

public IEnumerable<UserBandRelation> GetBandRelationsByUser(
    Expression<Func<UsersBand, bool>> predicate)
{
    using (var ctx = new OpenGroovesEntities())
    {
        var relations = ctx.UsersBands.Where(predicate);

        // mapping, other stuff, back to business layer
        return relations.ToList();
    }
}

The LINQ expression node type 'Invoke' is not supported in LINQ to Entities' when lambda is passed as a parameter, but not when used directly

An Expression object is compiled into a data structure (an expression tree). This is converted to SQL code at runtime by EF. A Func on the other hand is converted to executable IL code by the compiler. When you ask EF to translate a query that contains Where(x => f(x)), you have a Func f which is IL code, and a small expression tree around that, describing a call to the function represented by f. What the error message is saying is that this "Invoke" expression tree cannot be translated to SQL, which is reasonable since what is being invoked is a piece of IL code.

Note that in your first example where the Where call is inline, you're using an Expression, not a Func. This is because lambda expressions in C# can have both types, and when using the Where extension method on IQueryable, the parameter is of an Expression type, thus the entire lambda is compiled to an expression tree.

Error The LINQ expression node type 'Invoke' is not supported in LINQ to Entities in where clause inside the method

To do what you want you will need to do something like:

public static IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, int>> func)
{
    IQueryable<TEntity> res = source;

    if (!LBoundIsNull) 
    {
        Expression ge = Expression.GreaterThanOrEqual(func.Body, Expression.Constant(_lBound));
        var lambda = Expression.Lambda<Func<TEntity, bool>>(ge, func.Parameters);
        res = res.Where(lambda);
    }

    if (!UBoundIsNull)
    {
        Expression le = Expression.LessThanOrEqual(func.Body, Expression.Constant(_uBound));
        var lambda = Expression.Lambda<Func<TEntity, bool>>(le, func.Parameters);
        res = res.Where(lambda);
    }

    return res;
}

As you can see you'll need to do some expression-tree plumbing. You call the method in the same way as before.

Now... is it really possible to use LinqKit as suggested by @jbl? Yes... By shaking a little the magic wand...

using LinqKit;

public static IQueryable<TEntity> Compare<TEntity>(IQueryable<TEntity> source, Expression<Func<TEntity, int>> func)
{
    IQueryable<TEntity> res = source;

    if (!LBoundIsNull)
    {
        Expression<Func<TEntity, bool>> lambda = x => func.Invoke(x) >= _lBound;
        res = res.Where(lambda.Expand());
    }

    if (!UBoundIsNull)
    {
        Expression<Func<TEntity, bool>> lambda = x => func.Invoke(x) <= _uBound;
        res = res.Where(lambda.Expand());
    }

    return res;
}

Note the use of the Invoke() and Expand() LinqKit methods.

The LINQ expression node type 'Lambda' is not supported in LINQ to Entities

Use this:

var result = context.Corrects.Where(predicate);

instead of this:

var result = context.Corrects.Where(x => predicate == null);

Where expects argument of type Expression<Func<T, bool>>, but you're trying to pass Expression<Func<T, Expression<...>> instead. This is valid compile-time construct, but at run-time LINQ provider fails, when it tries to translate predicate to SQL.

Also note, that you should change Expression<Func<Correct, bool?>> into Expression<Func<Correct, bool>>.

Error: The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities

Under normal circumstances, when performing an operation like a Where in EntityFramework, it isn't actually executed in memory like when you operate on an enumerable (like a List). Instead, it converted into SQL which is then executed by the Db provider. This means that doing certain things, such as using extension methods on objects or, in your case, getting elements from arrays by index is not an option, as the converter cannot turn such things into SQL.

To fix your existing code, you need to modify your for loop like so:

for(int i = 0; i <= myArray.Length-1; i++)
{
    var temp = myArray[i].ToString();
    events = events.Where(u => u.AspNetUser.Id == temp);
}

Moving the array operation outside of the query allows EntityFramework to convert it into SQL properly.

A better approach to doing what you want would be the following:

var result = events.Where(u => myArray.Contains(u.AspNetUser.Id));

The LINQ expression node type 'NewArrayBounds' is not supported in LINQ to Entities

Initialize the array in an empty constructor of your class:

public class ProviderMeta
{
    //...
   public ProviderMeta()
   {
     Roles = new int[]{0};
   }
}

And remove it from the projection

 select new ProviderMeta
        {
            LoginId = user.LoginId,
            AgencyId = user.AgencyId,
            Application = user.Application,
            UserId = user.UserId,
            Name = agencySnapshot.Name,
            //Roles = new int[0], remove this line
            Cluster = app.ClusterId ?? 0,
            Created = app.Created,
            TitleType = user.TitleType,
            Feature = (foundFeature == null ? 0 : foundFeature.Feature)
        }).ToList();

Generic expression for where clause - The LINQ expression node type 'Invoke' is not supported in LINQ to Entities.

The problem, as you describe, is that the entityKey function in the first example is opaque since it is of type Func rather than Expression. However, you can get the behavior you want by implementing a Compose() method to combine two expressions. I posted the code to implement compose in this question: use Expression<Func<T,X>> in Linq contains extension.

With Compose() implemented, your function can be implemented as below:

public static List<T> Load<T>(this IQueryable<T> entityQuery, 
                              int[] entityIds, 
                              // note that this is an expression now
                              Expression<Func<T, int>> entityKey, 
                              int batchSize = 500, 
                              Expression<Func<T, bool>> postFilter = null) 
    where T : EntityObject
{
    Expression<Func<int, bool>> containsExpression = id => entityIds.Contains(id);
    Expression<Func<T, bool>> whereInEntityIdsExpression = containsExpression.Compose(entityKey);

    IQueryable<T> filteredById = entityQuery.Where(whereInEntityIdsExpression);

    // if your post filter is compilable to SQL, you might as well do the filtering
    // in the database
    if (postFilter != null) { filteredById = filteredById.Where(postFilter); }

    // finally, pull into memory
    return filteredById.ToList();
} 

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