使用LINQ-to-Entities返回对象集合，其中对象属性与另一个对象集合中的任何属性匹配 [英] Returning a collection of objects where an objects property matches any property from another collection of objects using LINQ-to-Entities

问题描述

我整天都在搜索，找不到解决方案...

I've been searching all day and can't find a solution to this...

我有一个EntityCollection个Communication个对象，每个对象都有一个Intention个对象的实例(一对一).

I have an EntityCollection of Communication objects which each have an instance of an Intention object(one-to-one).

我还有一个User对象，该对象具有UserLocation EntityObjects(一对多)

I also have a User object which has many instances of UserLocation EntityObjects(one-to-many)

• Intention对象具有属性UID.

• UserLocation对象具有属性LID.

• Intention objects have a property UID.

• UserLocation objects have a property LID.

我想编写一个LINQ表达式，该表达式返回所有Communication对象，其中与Communication对象关联的Intention实例的UID属性等于a的ANY实例的ANY LID属性User对象的UserLocation实例.

I want to write a LINQ expression which returns all Communication objects where the UID property of the Intention instance associated to a Communication object equals ANY LID property of ANY instance of a UserLocation instance for a User object.

我已经尝试过了

return _context.Communications.Where
(u => u.Intention.UID.Equals
(user.UserLocations.Select
(p => p.LID)));

还有这个

return _context.Communications.Where
(u => user.UserLocations.Any
(x => x.LID.Equals
(u.Intention.UID)));

还有这个

var thislist = from Intentions in _context.Intentions
                           join UserLocations in user.UserLocations
                           on Intentions.UID equals UserLocations.LID
                           select Intentions.UID;
            return _context.Communications.Where(u => u.Intention.Equals(thislist.Any()));

还有这个

var lidlist = user.UserLocations.Select(x => x.LID);
return _context.Communications.Where(x=> lidlist.Contains(x.Intention.UID)).ToList();

(这使我在Contains语句中出现了一个错误，说委托System.Func<Communication,int,bool>不带1个参数"，不知道如何解决)

(this gives me an error on the Contains statement saying "Delegate System.Func<Communication,int,bool> does not take 1 argument", don't know how to fix)

除了所有这些变化之外，我还拥有:

Along with all these variations I have also:

• 修改了我的方法以返回IQueryable<Communication>，并且在将ToList()附加到查询中时也尝试了List<Communication>.

• modified my method to return IQueryable<Communication> and have also tried List<Communication> while appending ToList() to my queries.

没有任何效果.不管我尝试什么，我总是会遇到这种例外情况

Nothing works. Regardless of what I try I always end up with this exception

NotSupportedException未通过用户代码处理

无法创建类型为'PreparisCore.BusinessEntities.UserLocation'的常量值.在这种情况下，仅支持基本类型(例如Int32，String和Guid).

我在做什么错??

推荐答案

给出以下代码:

namespace CollectionsWithIntentions
{
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.Linq;

    internal class Program
    {
        #region Methods

        private static void Main(string[] args)
        {
            var communications = new[]
                {
                    new Communication { Intention = new Intention { UID = 1 } },
                    new Communication { Intention = new Intention { UID = 2 } },
                    new Communication { Intention = new Intention { UID = 3 } },
                    new Communication { Intention = new Intention { UID = 4 } },
                };
            var users = new[]
                {
                    new User { UserLocations = new List<UserLocation>(new[] { new UserLocation { LID = 2 },new UserLocation{LID=5}  }) },
                    new User { UserLocations = new List<UserLocation>(new[] { new UserLocation { LID = 3 } }) }
                };

            IEnumerable<Communication> res =
                communications.Where(w => users.Any(a => a.UserLocations.Any(b=>b.LID == w.Intention.UID)));
            foreach (Communication communication in res)
            {
                Trace.WriteLine(communication);
            }
        }

        #endregion
    }

    internal class Communication
    {
        #region Public Properties

        public Intention Intention { get; set; }

        #endregion

        #region Public Methods and Operators

        public override string ToString()
        {
            return string.Concat("Communication-> Intention:", this.Intention.UID);
        }

        #endregion
    }

    internal class Intention
    {
        #region Public Properties

        public int UID { get; set; }

        #endregion
    }

    internal class User
    {
        #region Public Properties

        public List<UserLocation> UserLocations { get; set; }

        #endregion
    }

    internal class UserLocation
    {
        #region Public Properties

        public int LID { get; set; }

        #endregion
    }
}

我得到这个结果:

Communication-> Intention:2
Communication-> Intention:3

我想念什么吗?

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