无法获得多映射小巧玲珑工作 [英] Can't get multi-mapping to work in Dapper
问题描述
玩弄短小精悍，我很高兴的结果至今 - 耐人寻味
但是，现在，我的下一个情况是从两个表中读取数据 - 一个学生和地址表
学生表中有 StudentID（INT IDENTITY），地址有一个 AddressID（INT IDENTITY）。 学生也有称为FK AddressID 连接到地址表。
我的想法是创建两个类，每个表，用我感兴趣的。另外，我把属性的 PrimaryAddress 属性类型地址到在C＃我的学生类。
然后我想在一个单一的查询检索学生和地址数据 - 模拟天生我说的对的 Github的页面：
VAR数据=连接。查询<邮政，使用者>（SQL，（后，用户）=> {post.Owner =用户;}）;
无功后= data.First（）;
在这里，发表和用户检索，和后的所有者设置为用户 - 返回的类型是发表 - 正确？ / p>
所以，在我的代码，我定义两个参数，一般查询扩展方法 - 一个学生作为第一个应当返还，以及地址作为第二个，这将被存储到学生的实例：
VAR学生= _conn.Query<职业，地址>
（选S *，一。* FROM dbo.Student小号
INNER JOIN dbo.Address一个ON s.AddressID = a.AddressID
其中s.StudentenID = @Id
（STU，ADR）=> {stu.PrimaryAddress = ADR;}
新{ID = 4711}）;
麻烦的是 - 我得到在Visual Studio中的错误：
使用泛型方法
'Dapper.SqlMapper.Query（System.Data.IDbConnection，
字符串，
System.Func，
动感，System.Data.IDbTransaction，
布尔，字符串，整数？
System.Data.CommandType？）'需要6
类型参数
我真的不明白为什么小巧玲珑使用此重载6类型参数...
这是因为我改变了API和忘了更新的文档，我纠正了错误。
一定要看看的Tests.cs 的一个完整的先进的最新规范。
在特定的，以前需要在旧的API的动作< T，U> 来执行映射，麻烦的是，它感到既武断和缺乏灵活性。你不能完全控制的返回类型。新的API参加一个 Func键< T，U，V> 。所以，你可以控制你从后面映射器的类型，它并不需要是一个映射类型。
我只是绑住周围多映射一些额外的灵活性，这个测试应该清楚：
类Person
{
公众诠释PERSONID {搞定;组; }
公共字符串名称{;组; }
}
类地址
{
公众诠释AddressId {搞定;组; }
公共字符串名称{;组; }
公众诠释PERSONID {搞定;组; }
}
级额外
{
公众诠释标识{搞定;组; }
公共字符串名称{;组; }
}
公共无效TestFlexibleMultiMapping（）
{
变种的sql =
@，选择
1为PERSONID，'鲍勃'作为名称，
2作为AddressId，'ABC街作为名称，如1 PERSONID，
3为ID，弗雷德作为名称
;
VAR personWithAddress = connection.Query<人，地址，额外的，元组LT;人，地址，额外>>
（SQL，（P，A，E）=> Tuple.Create（P，A，E），splitOn：AddressId，ID）。首先（）;
personWithAddress.Item1.PersonId.IsEqualTo（1）;
personWithAddress.Item1.Name.IsEqualTo（鲍勃）;
personWithAddress.Item2.AddressId.IsEqualTo（2）;
personWithAddress.Item2.Name.IsEqualTo（ABC街）;
personWithAddress.Item2.PersonId.IsEqualTo（1）;
personWithAddress.Item3.Id.IsEqualTo（3）;
personWithAddress.Item3.Name.IsEqualTo（弗雷德）;
}
小巧玲珑的管道都通过一个单一的方法多的地图API，所以，如果事情失败，将在6参数作为结束语起来。另一块拼图是，我没有允许一些超级灵活的分裂，这是我刚才添加。
请注意，在 splitOn 参数将默认为编号，这意味着它会采取一个名为列 ID 或标识作为第一个对象的边界。然而，如果你需要上有说3路多映射不同的名称，多个主键的界限，现在你可以传递一个逗号分隔的列表。
所以，如果我们要解决上面，大概可以如下：
VAR学生= _conn.Query<职业，地址，学生>
（选S *，一。* FROM dbo.Student小号
INNER JOIN dbo.Address一个ON s.AddressID = a.AddressID
其中s.StudentenID = @Id
（STU，ADR）=> {stu.PrimaryAddress = ADR;返回STU;}
新{ID = 4711}，splitOn：AddressID）FirstOrDefault（）;
Playing around with Dapper, I'm quite pleased with the results so far - intriguing!
But now, my next scenario would be to read data from two tables - a Student and an Address table.
Student table has a primary key of StudentID (INT IDENTITY), Address has an AddressID (INT IDENTITY). Student also has an FK called AddressID linking into the Address table.
My idea was to create two classes, one for each table, with the properties I'm interested in. Additionally, I put an PrimaryAddress property of type Address onto my Student class in C#.
I then tried to retrieve both student and address data in a single query - I mimick the sample that's given on the Github page:
var data = connection.Query<Post, User>(sql, (post, user) => { post.Owner = user; });
var post = data.First();
Here, a Post and a User are retrieved, and the owner of the post is set to the user - the type returned is a Post - correct?
So in my code, I define two parameters to the generic Query extension method - a Student as the first which should be returned, and an Address as the second, which will be stored onto the student instance:
var student = _conn.Query<Student, Address>
("SELECT s.*, a.* FROM dbo.Student s
INNER JOIN dbo.Address a ON s.AddressID = a.AddressID
WHERE s.StudentenID = @Id",
(stu, adr) => { stu.PrimaryAddress = adr; },
new { Id = 4711 });
Trouble is - I get an error in Visual Studio:
Using the generic method 'Dapper.SqlMapper.Query(System.Data.IDbConnection, string, System.Func, dynamic, System.Data.IDbTransaction, bool, string, int?, System.Data.CommandType?)' requires 6 type arguments
I don't really understand why Dapper insists on using this overload with 6 type arguments...
That would be cause I changed APIs and forgot to update the documentation, I corrected the error.
Be sure to have a look at Tests.cs for a full up-to-date spec.
In particular, the old API used to take in an Action<T,U> to perform the mapping, the trouble was that it felt both arbitrary and inflexible. You could not fully control the return type. The new APIs take in a Func<T,U,V>. So you can control the type you get back from the mapper and it does not need to be a mapped type.
I just tied up some additional flexibility around multi mapping, this test should make it clear:
class Person
{
public int PersonId { get; set; }
public string Name { get; set; }
}
class Address
{
public int AddressId { get; set; }
public string Name { get; set; }
public int PersonId { get; set; }
}
class Extra
{
public int Id { get; set; }
public string Name { get; set; }
}
public void TestFlexibleMultiMapping()
{
var sql =
@"select
1 as PersonId, 'bob' as Name,
2 as AddressId, 'abc street' as Name, 1 as PersonId,
3 as Id, 'fred' as Name
";
var personWithAddress = connection.Query<Person, Address, Extra, Tuple<Person, Address,Extra>>
(sql, (p,a,e) => Tuple.Create(p, a, e), splitOn: "AddressId,Id").First();
personWithAddress.Item1.PersonId.IsEqualTo(1);
personWithAddress.Item1.Name.IsEqualTo("bob");
personWithAddress.Item2.AddressId.IsEqualTo(2);
personWithAddress.Item2.Name.IsEqualTo("abc street");
personWithAddress.Item2.PersonId.IsEqualTo(1);
personWithAddress.Item3.Id.IsEqualTo(3);
personWithAddress.Item3.Name.IsEqualTo("fred");
}
Dapper pipes all the multi mapping APIs through a single method, so if something fails it will end up in the 6 param one. The other piece of the puzzle was that I did not allow for some super flexible splits, which I just added.
Note, the splitOn param will default to Id, meaning it will take a column called id or Id as the first object boundary. However if you need boundaries on multiple primary keys that have different names for say a "3 way" multi mapping, you can now pass in a comma separated list.
So if we were to fix the above, probably the following would work:
var student = _conn.Query<Student,Address,Student>
("SELECT s.*, a.* FROM dbo.Student s
INNER JOIN dbo.Address a ON s.AddressID = a.AddressID
WHERE s.StudentenID = @Id",
(stu, adr) => { stu.PrimaryAddress = adr; return stu;},
new { Id = 4711 }, splitOn: "AddressID").FirstOrDefault();
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