我在使用join/where子句和一个相当简单的sql select语句苦苦挣扎.
I'm struggling with a join/where clause with what is a rather simple sql select statement.
我正在尝试从tb1检索产品信息列表,其中where条件位于tbl2中,但这必须由三个不同的列连接起来.
I am trying to retrieve a list of product information from tb1 with the where condition behind situated in tbl2 but this must be joined by three different columns.
因此SQL看起来类似于:
so the SQL would look something along the lines of:
SELECT tb1.* FROM tb2 INNER JOIN tb1 ON tb2.Col1 = tb1. Col1 AND tb2.Col2 = tb1. Col2 AND tb2.Col3 = tb1.Col3 WHERE (tb2.Col1 = col1) AND (tb2.Col2 = col2) AND (tb2.Col4 = string)ColX是主要的where子句,带有要作为参数传递的字符串;所有其他列都在上下文中.
ColX is the main where clause with the string to be passed in as parameter; all other columns are within the contexts.
如何使用where子句实现多个联接?
How do you implement multiple joins with a where clause?
朝正确的方向推,非常感谢.
And shoves in the right direction, muchly appreciated.
推荐答案要在LINQ中的多个字段上进行联接,您必须创建一个包含要比较的列的新匿名类型,然后在该联接中使用该匿名类型:
To join on multiple field in LINQ, you have to create a new anonymous type containing the columns you want to compare and then use that anonymous type in the join:
var results = from t1 in context.tb1 join t2 in context.tb2 on new { t1.Col1, t1.Col2, t1.Col3 } equals new { t2.Col1, t2.Col2, t2.Col3 } where t2.Col1 == col1 && t2.Col2 == col2 && t2.Col4 == someString select t1;这是等效的Lambda语法:
And here is the equivalent Lambda Syntax:
var results = context.tb1.Join( context.tb2, t1 => new { t1.Col1, t1.Col2, t1.Col3 }, t2 => new { t2.Col1, t2.Col2, t2.Col3 }, (t1, t2) => new { t1, t2 }) .Where(o => o.t2.Col1 == col1 && o.t2.Col2 == col2 && o.t2.Col4 == someString) .Select(o => o.t1);如您所见,对于联接,查询语法通常会产生易于阅读的语句.
As you can see, in the case of joins, query syntax usually produces an easier to read statement.
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