实体框架连接 3 个表 [英] Entity Framework Join 3 Tables

问题描述

我正在尝试连接三个表，但我无法理解该方法...

I'm trying to join three tables but I can't understand the method...

我完成了 2 个表的连接

I completed join 2 tables

        var entryPoint = dbContext.tbl_EntryPoint
            .Join(dbContext.tbl_Entry,
                c => c.EID,
                cm => cm.EID,
                (c, cm) => new
                {
                    UID = cm.OwnerUID,
                    TID = cm.TID,
                    EID = c.EID,
                }).
            Where(a => a.UID == user.UID).Take(10);

我想包含 tbl_Title 表和 TID PK 并获得 Title 字段.

I would like to include tbl_Title table with TID PK and get Title field.

非常感谢

推荐答案

这是未经测试的，但我相信语法应该适用于 lambda 查询.当您使用此语法连接更多表时，您必须进一步深入研究新对象以获取您想要操作的值.

This is untested, but I believe the syntax should work for a lambda query. As you join more tables with this syntax you have to drill further down into the new objects to reach the values you want to manipulate.

var fullEntries = dbContext.tbl_EntryPoint
    .Join(
        dbContext.tbl_Entry,
        entryPoint => entryPoint.EID,
        entry => entry.EID,
        (entryPoint, entry) => new { entryPoint, entry }
    )
    .Join(
        dbContext.tbl_Title,
        combinedEntry => combinedEntry.entry.TID,
        title => title.TID,
        (combinedEntry, title) => new 
        {
            UID = combinedEntry.entry.OwnerUID,
            TID = combinedEntry.entry.TID,
            EID = combinedEntry.entryPoint.EID,
            Title = title.Title
        }
    )
    .Where(fullEntry => fullEntry.UID == user.UID)
    .Take(10);

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