Dapper.NET-映射多对多数据库关系？

Question

I have 2 tables in SQL Server like this:

Table1
    int Id
    varchar(32) Name
    varchar(256) Description

Table2
    int LeftKey
    int RightKey

I have 2 classes in the C# application like:

MyClass
    Name
    Description

Match
    MyClass Left
    MyClass Right

What I want to do is create a Dapper query which will select all rows in Table2, joining to Table1 (*Key->Id) and produce a list of Match objects with the Left and Right properties set accordingly.

Is there a nice clean way of doing this with Dapper?

I've looked at other many to many questions on Stackoverflow and they all seem to differ from my scenario.

Answer 1

Dapper is really just a way of splitting a grid and quickly assigning columns to an object. It sounds like you just have the same object twice - one for left, one for right.

So...your sql might look like this:

select 
lk.*,
rk.*
from Table2 t2
inner join Table1 t1_left on t1_left.Id = t2.LeftKey
inner join Table1 t1_right on t1_right.Id = t2.RightKey

And your dapper might look like this:

connection.Query<MyClass,MyClass,Match>(sqlhere,(mc1,mc2)=>{

var match = new Match();
match.Left = mc1;
match.Right = mc2;

return match;

});

No need to return anything from Table2 in your sql, nor to automatically map it with Dapper. It's really just acting like a Tuple, so we can create it in the return func.