IQueryable<T> does not contain a definition for 'Include' and no extension method 'Include'

I'm trying to use Include extension on IQueryable set, but I have the following issue:

Error 1 'System.Linq.IQueryable<.Model.InsuranceCaseType>' does not contain a definition for 'Include' and no extension method 'Include' accepting a first argument of type 'System.Linq.IQueryable<.Model.InsuranceCaseType>' could be found (are you missing a using directive or an assembly reference?)

My code:

var allCaseTypes = Uow.InsuranceCaseType.GetAll().Include(a=>a.Geos);

Method GetAll() returns - IQueryable<.Model.InsuranceCaseType>

I have in scope the following namespaces:

using System.Collections;
using System.Collections.Generic;
using System;
using System.Data;
using System.Linq;
using System.Data.Entity;
using System.IO;
using System.Web;
using System.Web.Mvc;

Solution 1:

Include is not an extension method on Queryable, so it doesn't come together with all the usual LINQ methods. If you are using Entity Framework, you need to import the corresponding namespace:

using System.Data.Entity;

Solution 2:

If you are using .Net core version then you need to install: Microsoft.EntityFrameworkCore nuget package.

And then:

using Microsoft.EntityFrameworkCore;