我一直在玩这个，因为它看起来感觉很像documented posts/users example，但它略有不同，对我不起作用。
假设以下简化设置（联系人有多个电话号码）：
public class Contact
{
public int ContactID { get; set; }
public string ContactName { get; set; }
public IEnumerable<Phone> Phones { get; set; }
}
public class Phone
{
public int PhoneId { get; set; }
public int ContactID { get; set; } // foreign key
public string Number { get; set; }
public string Type { get; set; }
public bool IsActive { get; set; }
}
我希望最终能够返回与多个Phone对象联系的内容。这样，如果我有2个联系人，每个联系人有2个电话，我的SQL将返回一个连接，作为结果集共4行。然后Dapper将弹出2个联系人对象，每个联系对象有两部手机。
以下是存储过程中的SQL：
SELECT *
FROM Contacts
LEFT OUTER JOIN Phones ON Phones.ReferenceId=Contacts.ReferenceId
WHERE clientid=1
我尝试了这个，但结果是4个元组（这是好的，但不是我希望的...这只是意味着我仍然需要重新规范化结果）：
var x = cn.Query<Contact, Phone, Tuple<Contact, Phone>>("sproc_Contacts_SelectByClient",
(co, ph) => Tuple.Create(co, ph),
splitOn: "PhoneId", param: p,
commandType: CommandType.StoredProcedure);
当我尝试另一种方法（下面）时，我得到一个例外，“无法将类型'System.Int32'的对象强制转换为'System.Collections.Generic.IEnumerable`1 [Phone]'。”
var x = cn.Query<Contact, IEnumerable<Phone>, Contact>("sproc_Contacts_SelectByClient",
(co, ph) => { co.Phones = ph; return co; },
splitOn: "PhoneId", param: p,
commandType: CommandType.StoredProcedure);
我只是做错了吗？它似乎就像帖子/所有者的例子，除了我从父母到孩子而不是孩子到父母。
提前致谢
答案 0 :(得分：63)
你没有做错任何事，这不是API的设计方式。所有Query API将始终返回每个数据库行的对象。
所以，这对许多人来说效果很好 - ＆gt;一个方向，但对一个方向不太好 - ＆gt;许多多地图。
这里有两个问题：
如果我们引入一个与您的查询一起使用的内置映射器，我们将需要“丢弃”重复数据。 （联系人。*在您的查询中重复）
如果我们将其设计为使用一个 - >很多配对，我们需要某种身份地图。这增加了复杂性。
以此查询为例，如果您只需要提取有限数量的记录，如果您将其推高到一百万个变得更加棘手，导致您需要流式传输并且无法将所有内容加载到内存中，那么该查询是有效的：
var sql = "set nocount on
DECLARE @t TABLE(ContactID int, ContactName nvarchar(100))
INSERT @t
SELECT *
FROM Contacts
WHERE clientid=1
set nocount off
SELECT * FROM @t
SELECT * FROM Phone where ContactId in (select t.ContactId from @t t)"
您可以做的是扩展GridReader以允许重新映射：
var mapped = cnn.QueryMultiple(sql)
.Map<Contact,Phone, int>
(
contact => contact.ContactID,
phone => phone.ContactID,
(contact, phones) => { contact.Phones = phones };
);
假设您使用mapper扩展GridReader：
public static IEnumerable<TFirst> Map<TFirst, TSecond, TKey>
(
this GridReader reader,
Func<TFirst, TKey> firstKey,
Func<TSecond, TKey> secondKey,
Action<TFirst, IEnumerable<TSecond>> addChildren
)
{
var first = reader.Read<TFirst>().ToList();
var childMap = reader
.Read<TSecond>()
.GroupBy(s => secondKey(s))
.ToDictionary(g => g.Key, g => g.AsEnumerable());
foreach (var item in first)
{
IEnumerable<TSecond> children;
if(childMap.TryGetValue(firstKey(item), out children))
{
addChildren(item,children);
}
}
return first;
}
因为这有点棘手和复杂，有警告。我并不倾向于将其纳入核心。
答案 1 :(得分：30)
仅供参考 - 我通过以下方式获得了Sam的回答：
首先，我添加了一个名为“Extensions.cs”的类文件。我必须在两个地方将“this”关键字更改为“reader”：
using System;
using System.Collections.Generic;
using System.Linq;
using Dapper;
namespace TestMySQL.Helpers
{
public static class Extensions
{
public static IEnumerable<TFirst> Map<TFirst, TSecond, TKey>
(
this Dapper.SqlMapper.GridReader reader,
Func<TFirst, TKey> firstKey,
Func<TSecond, TKey> secondKey,
Action<TFirst, IEnumerable<TSecond>> addChildren
)
{
var first = reader.Read<TFirst>().ToList();
var childMap = reader
.Read<TSecond>()
.GroupBy(s => secondKey(s))
.ToDictionary(g => g.Key, g => g.AsEnumerable());
foreach (var item in first)
{
IEnumerable<TSecond> children;
if (childMap.TryGetValue(firstKey(item), out children))
{
addChildren(item, children);
}
}
return first;
}
}
}
其次，我添加了以下方法，修改了最后一个参数：
public IEnumerable<Contact> GetContactsAndPhoneNumbers()
{
var sql = @"
SELECT * FROM Contacts WHERE clientid=1
SELECT * FROM Phone where ContactId in (select ContactId FROM Contacts WHERE clientid=1)";
using (var connection = GetOpenConnection())
{
var mapped = connection.QueryMultiple(sql)
.Map<Contact,Phone, int> (
contact => contact.ContactID,
phone => phone.ContactID,
(contact, phones) => { contact.Phones = phones; }
);
return mapped;
}
}
答案 2 :(得分：20)
结帐https://www.tritac.com/blog/dappernet-by-example/ 你可以这样做：
public class Shop {
public int? Id {get;set;}
public string Name {get;set;}
public string Url {get;set;}
public IList<Account> Accounts {get;set;}
}
public class Account {
public int? Id {get;set;}
public string Name {get;set;}
public string Address {get;set;}
public string Country {get;set;}
public int ShopId {get;set;}
}
var lookup = new Dictionary<int, Shop>()
conn.Query<Shop, Account, Shop>(@"
SELECT s.*, a.*
FROM Shop s
INNER JOIN Account a ON s.ShopId = a.ShopId
", (s, a) => {
Shop shop;
if (!lookup.TryGetValue(s.Id, out shop)) {
lookup.Add(s.Id, shop = s);
}
shop.Accounts.Add(a);
return shop;
},
).AsQueryable();
var resultList = lookup.Values;
我从dapper.net测试中得到了这个：https://code.google.com/p/dapper-dot-net/source/browse/Tests/Tests.cs#1343
答案 3 :(得分：10)
在您的情况下，拥有多结果集查询会更好（也更容易）。这只是意味着您应该编写两个select语句：
这样你的对象就是唯一的，不会重复。
答案 4 :(得分：10)
这是一个非常易于使用的可重用解决方案。这是Andrews answer的略微修改。
public static IEnumerable<TParent> QueryParentChild<TParent, TChild, TParentKey>(
this IDbConnection connection,
string sql,
Func<TParent, TParentKey> parentKeySelector,
Func<TParent, IList<TChild>> childSelector,
dynamic param = null, IDbTransaction transaction = null, bool buffered = true, string splitOn = "Id", int? commandTimeout = null, CommandType? commandType = null)
{
Dictionary<TParentKey, TParent> cache = new Dictionary<TParentKey, TParent>();
connection.Query<TParent, TChild, TParent>(
sql,
(parent, child) =>
{
if (!cache.ContainsKey(parentKeySelector(parent)))
{
cache.Add(parentKeySelector(parent), parent);
}
TParent cachedParent = cache[parentKeySelector(parent)];
IList<TChild> children = childSelector(cachedParent);
children.Add(child);
return cachedParent;
},
param as object, transaction, buffered, splitOn, commandTimeout, commandType);
return cache.Values;
}
使用示例
public class Contact
{
public int ContactID { get; set; }
public string ContactName { get; set; }
public List<Phone> Phones { get; set; } // must be IList
public Contact()
{
this.Phones = new List<Phone>(); // POCO is responsible for instantiating child list
}
}
public class Phone
{
public int PhoneID { get; set; }
public int ContactID { get; set; } // foreign key
public string Number { get; set; }
public string Type { get; set; }
public bool IsActive { get; set; }
}
conn.QueryParentChild<Contact, Phone, int>(
"SELECT * FROM Contact LEFT OUTER JOIN Phone ON Contact.ContactID = Phone.ContactID",
contact => contact.ContactID,
contact => contact.Phones,
splitOn: "PhoneId");
答案 5 :(得分：7)
基于Sam Saffron（和Mike Gleason的）方法，这里有一个解决方案，允许多个孩子和多个级别。
using System;
using System.Collections.Generic;
using System.Linq;
using Dapper;
namespace TestMySQL.Helpers
{
public static class Extensions
{
public static IEnumerable<TFirst> MapChild<TFirst, TSecond, TKey>
(
this SqlMapper.GridReader reader,
List<TFirst> parent,
List<TSecond> child,
Func<TFirst, TKey> firstKey,
Func<TSecond, TKey> secondKey,
Action<TFirst, IEnumerable<TSecond>> addChildren
)
{
var childMap = child
.GroupBy(secondKey)
.ToDictionary(g => g.Key, g => g.AsEnumerable());
foreach (var item in parent)
{
IEnumerable<TSecond> children;
if (childMap.TryGetValue(firstKey(item), out children))
{
addChildren(item, children);
}
}
return parent;
}
}
}
然后你可以在函数之外读取它。
using (var multi = conn.QueryMultiple(sql))
{
var contactList = multi.Read<Contact>().ToList();
var phoneList = multi.Read<Phone>().ToList;
contactList = multi.MapChild
(
contactList,
phoneList,
contact => contact.Id,
phone => phone.ContactId,
(contact, phone) => {contact.Phone = phone;}
).ToList();
return contactList;
}
然后可以使用相同的父对象再次为下一个子对象调用map函数。您还可以独立于map函数在父或子read语句上实现splits。
这是“单对N”附加扩展方法
public static TFirst MapChildren<TFirst, TSecond, TKey>
(
this SqlMapper.GridReader reader,
TFirst parent,
IEnumerable<TSecond> children,
Func<TFirst, TKey> firstKey,
Func<TSecond, TKey> secondKey,
Action<TFirst, IEnumerable<TSecond>> addChildren
)
{
if (parent == null || children == null || !children.Any())
{
return parent;
}
Dictionary<TKey, IEnumerable<TSecond>> childMap = children
.GroupBy(secondKey)
.ToDictionary(g => g.Key, g => g.AsEnumerable());
if (childMap.TryGetValue(firstKey(parent), out IEnumerable<TSecond> foundChildren))
{
addChildren(parent, foundChildren);
}
return parent;
}
答案 6 :(得分：1)
我想分享我对这个问题的解决方案，看看是否有人对我使用的方法有任何建设性的反馈？
我正在处理的项目中有一些要求，我需要先解释一下：
所以，我所做的就是让SQL通过返回一个单个JSON字符串作为原始行上的一列来处理第二级别层次结构（剥离其他列/属性等来说明）：
Id AttributeJson
4 [{Id:1,Name:"ATT-NAME",Value:"ATT-VALUE-1"}]
然后，我的POCO构建如下：
public abstract class BaseEntity
{
[KeyAttribute]
public int Id { get; set; }
}
public class Client : BaseEntity
{
public List<ClientAttribute> Attributes{ get; set; }
}
public class ClientAttribute : BaseEntity
{
public string Name { get; set; }
public string Value { get; set; }
}
POCO继承BaseEntity的地方。 （为了说明我选择了一个相当简单的单级层次结构，如客户端对象的“Attributes”属性所示。）
然后，我在数据层中有以下“数据类”，它继承自POCO Client。
internal class dataClient : Client
{
public string AttributeJson
{
set
{
Attributes = value.FromJson<List<ClientAttribute>>();
}
}
}
正如您在上面所看到的，发生的事情是SQL返回一个名为“AttributeJson”的列，该列映射到dataClient类中的属性AttributeJson。这只有一个setter，它将JSON反序列化为继承的Attributes类的Client属性。 dataClient类是internal到数据访问层，ClientProvider（我的数据工厂）将原始客户端POCO返回到调用App / Library，如下所示：
var clients = _conn.Get<dataClient>();
return clients.OfType<Client>().ToList();
请注意，我正在使用Dapper.Contrib并添加了一个新的Get<T>方法，该方法返回IEnumerable<T>
此解决方案有几点需要注意：
JSON序列化有明显的性能折衷 - 我已经对1050行进行了基准测试，其中有2个子List<T>属性，每个属性在列表中有2个实体，它的时钟频率为279ms - 对于我的项目需求是可以接受的 - 这也是在SQL方面的ZERO优化，所以我应该能够在那里刮几毫秒。
这确实意味着需要额外的SQL查询来为每个必需的List<T>属性构建JSON，但同样，这也适合我，因为我非常了解SQL并且在动态/反射方面不是那么流利等等。所以这种方式让我觉得我对事情有了更多的控制权，因为我实际上了解了幕后发生的事情： - ）
可能有一个比这个更好的解决方案，如果有，我真的很感激听到你的想法 - 这只是我提出的解决方案，到目前为止符合我对这个项目的需求（虽然这是实验性的发布阶段）。
答案 7 :(得分：0)
一旦我们决定将DataAccessLayer移到存储过程中，这些过程通常会返回多个链接结果（下面的示例）。
好吧，我的方法几乎相同，但也许会更舒服。
这是您的代码的样子：
using ( var conn = GetConn() )
{
var res = await conn
.StoredProc<Person>( procName, procParams )
.Include<Book>( ( p, b ) => p.Books = b.Where( x => x.PersonId == p.Id ).ToList() )
.Include<Course>( ( p, c ) => p.Courses = c.Where( x => x.PersonId == p.Id ).ToList() )
.Include<Course, Mark>( ( c, m ) => c.Marks = m.Where( x => x.CourseId == c.Id ).ToList() )
.Execute();
}
扩展名：
public static class SqlExtensions
{
public static StoredProcMapper<T> StoredProc<T>( this SqlConnection conn, string procName, object procParams )
{
return StoredProcMapper<T>
.Create( conn )
.Call( procName, procParams );
}
}
映射器：
public class StoredProcMapper<T>
{
public static StoredProcMapper<T> Create( SqlConnection conn )
{
return new StoredProcMapper<T>( conn );
}
private List<MergeInfo> _merges = new List<MergeInfo>();
public SqlConnection Connection { get; }
public string ProcName { get; private set; }
public object Parameters { get; private set; }
private StoredProcMapper( SqlConnection conn )
{
Connection = conn;
_merges.Add( new MergeInfo( typeof( T ) ) );
}
public StoredProcMapper<T> Call( object procName, object parameters )
{
ProcName = procName.ToString();
Parameters = parameters;
return this;
}
public StoredProcMapper<T> Include<TChild>( MergeDelegate<T, TChild> mapper )
{
return Include<T, TChild>( mapper );
}
public StoredProcMapper<T> Include<TParent, TChild>( MergeDelegate<TParent, TChild> mapper )
{
_merges.Add( new MergeInfo<TParent, TChild>( mapper ) );
return this;
}
public async Task<List<T>> Execute()
{
if ( string.IsNullOrEmpty( ProcName ) )
throw new Exception( $"Procedure name not specified! Please use '{nameof(Call)}' method before '{nameof( Execute )}'" );
var gridReader = await Connection.QueryMultipleAsync(
ProcName, Parameters, commandType: CommandType.StoredProcedure );
foreach ( var merge in _merges )
{
merge.Result = gridReader
.Read( merge.Type )
.ToList();
}
foreach ( var merge in _merges )
{
if ( merge.ParentType == null )
continue;
var parentMerge = _merges.FirstOrDefault( x => x.Type == merge.ParentType );
if ( parentMerge == null )
throw new Exception( $"Wrong parent type '{merge.ParentType.FullName}' for type '{merge.Type.FullName}'." );
foreach ( var parent in parentMerge.Result )
{
merge.Merge( parent, merge.Result );
}
}
return _merges
.First()
.Result
.Cast<T>()
.ToList();
}
private class MergeInfo
{
public Type Type { get; }
public Type ParentType { get; }
public IEnumerable Result { get; set; }
public MergeInfo( Type type, Type parentType = null )
{
Type = type;
ParentType = parentType;
}
public void Merge( object parent, IEnumerable children )
{
MergeInternal( parent, children );
}
public virtual void MergeInternal( object parent, IEnumerable children )
{
}
}
private class MergeInfo<TParent, TChild> : MergeInfo
{
public MergeDelegate<TParent, TChild> Action { get; }
public MergeInfo( MergeDelegate<TParent, TChild> mergeAction )
: base( typeof( TChild ), typeof( TParent ) )
{
Action = mergeAction;
}
public override void MergeInternal( object parent, IEnumerable children )
{
Action( (TParent)parent, children.Cast<TChild>() );
}
}
public delegate void MergeDelegate<TParent, TChild>( TParent parent, IEnumerable<TChild> children );
}
仅此而已，但是如果您想进行快速测试，以下是适合您的模型和步骤：
型号：
public class Person
{
public Guid Id { get; set; }
public string Name { get; set; }
public List<Course> Courses { get; set; }
public List<Book> Books { get; set; }
public override string ToString() => Name;
}
public class Book
{
public Guid Id { get; set; }
public Guid PersonId { get; set; }
public string Name { get; set; }
public override string ToString() => Name;
}
public class Course
{
public Guid Id { get; set; }
public Guid PersonId { get; set; }
public string Name { get; set; }
public List<Mark> Marks { get; set; }
public override string ToString() => Name;
}
public class Mark
{
public Guid Id { get; set; }
public Guid CourseId { get; set; }
public int Value { get; set; }
public override string ToString() => Value.ToString();
}
SP：
if exists (
select *
from sysobjects
where
id = object_id(N'dbo.MultiTest')
and ObjectProperty( id, N'IsProcedure' ) = 1 )
begin
drop procedure dbo.MultiTest
end
go
create procedure dbo.MultiTest
@PersonId UniqueIdentifier
as
begin
declare @tmpPersons table
(
Id UniqueIdentifier,
Name nvarchar(50)
);
declare @tmpBooks table
(
Id UniqueIdentifier,
PersonId UniqueIdentifier,
Name nvarchar(50)
)
declare @tmpCourses table
(
Id UniqueIdentifier,
PersonId UniqueIdentifier,
Name nvarchar(50)
)
declare @tmpMarks table
(
Id UniqueIdentifier,
CourseId UniqueIdentifier,
Value int
)
--------------------------------------------------
insert into @tmpPersons
values
( '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Иван' ),
( '467953a5-cb5f-4d06-9fad-505b3bba2058', N'Василий' ),
( '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'Алефтина' )
insert into @tmpBooks
values
( NewId(), '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Книга Математика' ),
( NewId(), '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Книга Физика' ),
( NewId(), '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Книга Геометрия' ),
( NewId(), '467953a5-cb5f-4d06-9fad-505b3bba2058', N'Книга Биология' ),
( NewId(), '467953a5-cb5f-4d06-9fad-505b3bba2058', N'Книга Химия' ),
( NewId(), '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'Книга История' ),
( NewId(), '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'Книга Литература' ),
( NewId(), '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'Книга Древне-шумерский диалект иврита' )
insert into @tmpCourses
values
( '30945b68-a6ef-4da8-9a35-d3b2845e7de3', '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Математика' ),
( '7881f090-ccd6-4fb9-a1e0-ff4ff5c18450', '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Физика' ),
( '92bbefd1-9fec-4dc7-bb58-986eadb105c8', '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'Геометрия' ),
( '923a2f0c-c5c7-4394-847c-c5028fe14711', '467953a5-cb5f-4d06-9fad-505b3bba2058', N'Биология' ),
( 'ace50388-eb05-4c46-82a9-5836cf0c988c', '467953a5-cb5f-4d06-9fad-505b3bba2058', N'Химия' ),
( '53ea69fb-6cc4-4a6f-82c2-0afbaa8cb410', '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'История' ),
( '7290c5f7-1000-4f44-a5f0-6a7cf8a8efab', '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'Литература' ),
( '73ac366d-c7c2-4480-9513-28c17967db1a', '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'Древне-шумерский диалект иврита' )
insert into @tmpMarks
values
( NewId(), '30945b68-a6ef-4da8-9a35-d3b2845e7de3', 98 ),
( NewId(), '30945b68-a6ef-4da8-9a35-d3b2845e7de3', 87 ),
( NewId(), '30945b68-a6ef-4da8-9a35-d3b2845e7de3', 76 ),
( NewId(), '7881f090-ccd6-4fb9-a1e0-ff4ff5c18450', 89 ),
( NewId(), '7881f090-ccd6-4fb9-a1e0-ff4ff5c18450', 78 ),
( NewId(), '7881f090-ccd6-4fb9-a1e0-ff4ff5c18450', 67 ),
( NewId(), '92bbefd1-9fec-4dc7-bb58-986eadb105c8', 79 ),
( NewId(), '92bbefd1-9fec-4dc7-bb58-986eadb105c8', 68 ),
( NewId(), '92bbefd1-9fec-4dc7-bb58-986eadb105c8', 75 ),
----------
( NewId(), '923a2f0c-c5c7-4394-847c-c5028fe14711', 198 ),
( NewId(), '923a2f0c-c5c7-4394-847c-c5028fe14711', 187 ),
( NewId(), '923a2f0c-c5c7-4394-847c-c5028fe14711', 176 ),
( NewId(), 'ace50388-eb05-4c46-82a9-5836cf0c988c', 189 ),
( NewId(), 'ace50388-eb05-4c46-82a9-5836cf0c988c', 178 ),
( NewId(), 'ace50388-eb05-4c46-82a9-5836cf0c988c', 167 ),
----------
( NewId(), '53ea69fb-6cc4-4a6f-82c2-0afbaa8cb410', 8 ),
( NewId(), '53ea69fb-6cc4-4a6f-82c2-0afbaa8cb410', 7 ),
( NewId(), '53ea69fb-6cc4-4a6f-82c2-0afbaa8cb410', 6 ),
( NewId(), '7290c5f7-1000-4f44-a5f0-6a7cf8a8efab', 9 ),
( NewId(), '7290c5f7-1000-4f44-a5f0-6a7cf8a8efab', 8 ),
( NewId(), '7290c5f7-1000-4f44-a5f0-6a7cf8a8efab', 7 ),
( NewId(), '73ac366d-c7c2-4480-9513-28c17967db1a', 9 ),
( NewId(), '73ac366d-c7c2-4480-9513-28c17967db1a', 8 ),
( NewId(), '73ac366d-c7c2-4480-9513-28c17967db1a', 5 )
--------------------------------------------------
select * from @tmpPersons
select * from @tmpBooks
select * from @tmpCourses
select * from @tmpMarks
end
go
答案 8 :(得分：0)
使用这个：
public class Product
{
public int ProductId { get; set; }
public string ProductName { get; set; }
public Category Category { get; set; }
}
public class Category
{
public int CategoryId { get; set; }
public string CategoryName { get; set; }
public ICollection<Product> Products { get; set; }
}
using (var connection = new SQLiteConnection(connString))
{
var sql = @"select productid, productname, p.categoryid, categoryname
from products p
inner join categories c on p.categoryid = c.categoryid";
var products = await connection.QueryAsync<Product, Category, Product>(sql, (product, category) => {
product.Category = category;
return product;
},
splitOn: "CategoryId");
products.ToList().ForEach(product => Console.WriteLine($"Product: {product.ProductName}, Category: {product.Category.CategoryName}"));
Console.ReadLine();
}