模拟跨上下文连接 - LINQ / C＃ [英] Simulating Cross Context Joins--LINQ/C#

问题描述

下面的问题：

我有2个数据的上下文，我愿做一个连接上。现在我知道，LINQ不允许从一个环境到另一个连接，我知道2个可能的解决办法是要么建立一个单一的DataContext或有2个独立的查询（这是我在做什么现在）。不过，我想要做的就是模拟的联接。

下面是我已经试过。

 使用（VAR _baseDataContext =实例）
{
    VAR查询从A =在_baseDataContext.Account.ACCOUNTs
                其中，a.STR_ACCOUNT_NUMBER.ToString（）==帐户ID
                加入应用在_baseDataContext.Account.APPLICATIONs上a.GUID_ACCOUNT_ID等于
                            app.GUID_ACCOUNT
                加入l在GetLoans（）上app.GUID_APPLICATION等于l.GUID_APPLICATION
                选择l.GUID_LOAN;    返回query.Count（）＆GT; 0？ query.First（）：Guid.Empty;
}私有静态的IQueryable＆LT;借贷和GT; GetLoans（）
{
    使用（VAR _baseDataContext =实例）
    {
        返回（从升的_baseDataContext.Loan.LOANs
                选择L）.AsQueryable（）;
    }
}
 

在运行时，我得到的是

System.InvalidOperationException：该查询包含对不同数据上下文定义的项目引用

编辑：

工作方案：

 使用（VAR _baseDataContext =实例）
{
    VAR查询从A =在_baseDataContext.Account.ACCOUNTs
                其中，a.STR_ACCOUNT_NUMBER.ToString（）==帐户ID
                加入应用在_baseDataContext.Account.APPLICATIONs上a.GUID_ACCOUNT_ID等于
                           app.GUID_ACCOUNT
                加入l在GetLoans（）上app.GUID_APPLICATION等于l.GUID_APPLICATION
                选择l.GUID_LOAN;     返回（query.Count（）＆0）？ query.First（）：Guid.Empty;
}私有静态的IEnumerable＆LT;借贷和GT; GetLoans（）
{
    使用（VAR _baseDataContext =实例）
    {
        返回（从升的_baseDataContext.Loan.LOANs
                选择L）.AsQueryable（）;
    }
}
 

解决方案

也许这样的事情可以让你在正确的方向开始。我做了基于列名类似列模拟数据库，并得到了一定的成效。

 类节目
{
    静态AccountContextDataContext aContext =新AccountContextDataContext（@数据源=;初始目录=;集成安全性=真）;
    静态LoanContextDataContext lContext =新LoanContextDataContext（@数据源=;初始目录=;集成安全性=真）;    静态无效的主要（）
    {        VAR查询从A =在aContext.ACCOUNTs
                    加入应用在aContext.APPLICATIONs上a.GUID_ACCOUNT_ID等于app.GUID_ACCOUNT
                    其中，app.GUID_APPLICATION.ToString（）==24551D72-D4C2-428B-84BA-5837A25D8CF6
                    选择GetLoans（app.GUID_APPLICATION）;        IEnumerable的＆LT;借贷和GT;贷款= query.First（）;
        的foreach（贷款贷款枚举）
        {
            Console.WriteLine（enumerable.GUID_LOAN）;
        }        到Console.ReadLine（）;
    }    私有静态的IEnumerable＆LT;借贷和GT; GetLoans（GUID applicationGuid）
    {
        返回（从升的lContext.LOANs那里l.GUID_APPLICATION == applicationGuid选择L）.AsQueryable（）;
    }
}
 

希望这有助于！

Here's the issue:

I have 2 data contexts that I would like to do a join on. Now I know that LINQ doesn't allow joins from one context to another, and I know that 2 possible solutions would be to either create a single datacontext or to have 2 seperate queries (which is what I'm doing for now). However what I would like to do is to "simulate" a join.

Here's what I've tried.

using (var _baseDataContext = Instance)
{
    var query = from a in _baseDataContext.Account.ACCOUNTs
                where a.STR_ACCOUNT_NUMBER.ToString() == accountID
                join app in _baseDataContext.Account.APPLICATIONs on a.GUID_ACCOUNT_ID equals
                            app.GUID_ACCOUNT
                join l in GetLoans() on app.GUID_APPLICATION equals l.GUID_APPLICATION
                select l.GUID_LOAN;

    return query.Count() > 0 ? query.First() : Guid.Empty;
}

private static IQueryable<LOAN> GetLoans()
{
    using (var _baseDataContext = Instance)
    {
        return (from l in _baseDataContext.Loan.LOANs
                select l).AsQueryable();
    }
}

In run time I get is

System.InvalidOperationException: The query contains references to items defined on a different data context

EDIT:

Working Solution:

using (var _baseDataContext = Instance)
{
    var query = from a in _baseDataContext.Account.ACCOUNTs
                where a.STR_ACCOUNT_NUMBER.ToString() == accountID
                join app in _baseDataContext.Account.APPLICATIONs on a.GUID_ACCOUNT_ID equals
                           app.GUID_ACCOUNT
                join l in GetLoans() on app.GUID_APPLICATION equals l.GUID_APPLICATION 
                select l.GUID_LOAN;

     return (query.Count() > 0) ? query.First() : Guid.Empty;
}

private static IEnumerable<LOAN> GetLoans()
{
    using (var _baseDataContext = Instance)
    {
        return (from l in _baseDataContext.Loan.LOANs
                select l).AsQueryable();
    }
}

解决方案

Maybe something like this can get you started in the right direction. I made a mock database with similar columns based on your column names and got some results.

    class Program
{
    static AccountContextDataContext aContext = new AccountContextDataContext(@"Data Source=;Initial Catalog=;Integrated Security=True");
    static LoanContextDataContext lContext = new LoanContextDataContext(@"Data Source=;Initial Catalog=;Integrated Security=True");

    static void Main()
    {

        var query = from a in aContext.ACCOUNTs
                    join app in aContext.APPLICATIONs on a.GUID_ACCOUNT_ID equals app.GUID_ACCOUNT
                    where app.GUID_APPLICATION.ToString() == "24551D72-D4C2-428B-84BA-5837A25D8CF6"
                    select GetLoans(app.GUID_APPLICATION);

        IEnumerable<LOAN> loan = query.First();
        foreach (LOAN enumerable in loan)
        {
            Console.WriteLine(enumerable.GUID_LOAN);
        }

        Console.ReadLine();
    }

    private static IEnumerable<LOAN> GetLoans(Guid applicationGuid)
    {
        return (from l in lContext.LOANs where l.GUID_APPLICATION == applicationGuid select l).AsQueryable();
    }
}

Hope this helps!

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