Multi-Mapper用于创建对象层次结构

Question

我一直在玩这个,因为它看起来感觉很像记录的帖子/用户示例,但它略有不同,并不适合我.

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一个与多个Phone对象联系的东西.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个接触对象,每个接触对象有两部手机.

这是存储过程中的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...它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(见下文),我得到的一个异常"无法投类型'System.Int32’的对象为类型'System.Collections.Generic.IEnumerable`1 [电话]’".

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

Answer 1

你没有做错任何事,这不是API的设计方式.所有QueryAPI将始终为每个数据库行返回一个对象.

因此,这在很多 - >一个方向上运行良好,但对于一个方向不太好 - >多个多地图.

这里有两个问题:

1. 如果我们引入一个适用于您的查询的内置映射器,我们将需要"丢弃"重复数据.(联系人.*在您的查询中重复)

2. 如果我们将它设计为使用一对 - >多对,我们将需要某种身份映射.这增加了复杂性.

例如,如果您只需要提取有限数量的记录,那么这个查询是有效的,如果您将其推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:

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 };  
    );

假设您扩展GridReader并使用映射器:

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.

Answer 2

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;
    }
}

Answer 3

查看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

Answer 4

多结果集支持

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:

1. 一个返回联系人
2. 还有一个可以返回电话号码的人

这样,您的对象将是唯一的,不会重复.

Answer 5

这是一个易于使用的可重用解决方案.这是对安德鲁斯答案的略微修改.

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;
}

用法示例

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");

Answer 6

基于Sam Saffron(和Mike Gleason的)方法,这里有一个允许多个孩子和多个级别的解决方案.

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;
        }
    }
}

然后你可以在函数外面读取它.

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语句上实现拆分.

这是一个"单对N"的附加扩展方法

    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;
    }

Answer 7

一旦我们决定将我们的 DataAccessLayer 移到存储过程中，而这些过程通常会返回多个链接的结果（示例如下）。

嗯，我的方法几乎相同，但可能更舒服一点。

您的代码可能如下所示：

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();
}

让我们分解它...

延期：

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 );
}

这就是全部，但如果您想进行快速测试，这里有适合您的模型和程序：

楷模：

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'????' ),
        ( '467953a5-cb5f-4d06-9fad-505b3bba2058', N'???????' ),
        ( '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'????????' )


    insert into @tmpBooks
    values
        ( NewId(), '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'????? ??????????' ),
        ( NewId(), '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'????? ??????' ),
        ( NewId(), '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'????? ?????????' ),

        ( NewId(), '467953a5-cb5f-4d06-9fad-505b3bba2058', N'????? ????????' ),
        ( NewId(), '467953a5-cb5f-4d06-9fad-505b3bba2058', N'????? ?????' ),

        ( NewId(), '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'????? ???????' ),
        ( NewId(), '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'????? ??????????' ),
        ( NewId(), '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'????? ??????-????????? ??????? ??????' )


    insert into @tmpCourses
    values
        ( '30945b68-a6ef-4da8-9a35-d3b2845e7de3', '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'??????????' ),
        ( '7881f090-ccd6-4fb9-a1e0-ff4ff5c18450', '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'??????' ),
        ( '92bbefd1-9fec-4dc7-bb58-986eadb105c8', '576fb8e8-41a2-43a9-8e77-a8213aa6e387', N'?????????' ),

        ( '923a2f0c-c5c7-4394-847c-c5028fe14711', '467953a5-cb5f-4d06-9fad-505b3bba2058', N'????????' ),
        ( 'ace50388-eb05-4c46-82a9-5836cf0c988c', '467953a5-cb5f-4d06-9fad-505b3bba2058', N'?????' ),

        ( '53ea69fb-6cc4-4a6f-82c2-0afbaa8cb410', '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'???????' ),
        ( '7290c5f7-1000-4f44-a5f0-6a7cf8a8efab', '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'??????????' ),
        ( '73ac366d-c7c2-4480-9513-28c17967db1a', '52a719bf-6f1f-48ac-9e1f-4532cfc70d96', N'??????-????????? ??????? ??????' )

    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