LINQ Lambda Join错误-无法从使用情况推断出 [英] LINQ Lambda Join Error - cannot be inferred from the usage

问题描述

我在加入两个DbSet时遇到麻烦，并继续收到无法推断的错误".我努力寻找一个解决方案，所以我想我会分享我的简单答案.乔恩·斯凯特(Jon Skeet)等人发表了好几篇好文章，但大多数答案都在我头上.

I had troubles joining two DbSets and continued to receive the "cannot be inferred error". I struggled to find a solution so I thought I would share my simple answer. There are several great posts from Jon Skeet and others but most of the answers were over my head.

以下是引起我麻烦的代码:

Here is the code that was causing me trouble:

using(var db = new SomeDataContext())
    {
    db.DemandData
        .Where(demand=> demand.ID == SearchID)
        .Join(db.CUST_ORDER_LINE,
            supply=> new { supply.LINE, supply.SALES_ORDER_ID },
            demand=> new { demand.LINE_NO, demand.CUST_ORDER_ID },
            (supply, demand) => new { custOrderLineReturn = demand })
        .Select(s => s.custOrderLineReturn )
        .ToList();
    }

推荐答案

我已经进行了很多次此联接，以至于直到找到贾斯汀·尼斯纳(Justin Niessner)的帖子匿名类型(以及它们的类型)中的属性名称必须完全匹配." 那把我引到了这段代码:

I have done this join so many times that I could not figure out why it would not work until I found a post from Justin Niessner here that says "The names of the properties in the anonymous types (as well as their types) must match exactly." That lead me to this code:

using(var db = new SomeDataContext())
    {
  return db.DemandData
        .Where(demand=> demand.ID == SearchID)
        .Join(db.CUST_ORDER_LINE,
            supply=> new { LINE_NO = supply.LINE, CUST_ORDER_ID = supply.SALES_ORDER_ID },
            demand=> new { demand.LINE_NO, demand.CUST_ORDER_ID },
            (supply, demand) => new { custOrderLineReturn = demand })
        .Select(s => s.custOrderLineReturn )
        .ToList();
    }

在第六行中，添加了与第七行中的字段名称匹配的变量 LINE_NO = 和 CUST_ORDER_ID = .

In the sixth line I added variables LINE_NO = and CUST_ORDER_ID = that matched the field names in line seven.

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