Multi-Mapper to create object hierarchy

user_331855 0
Viewed 58111

I've been playing around with this for a bit, because it seems like it feels a lot like the documented posts/users example, but its slightly different and isn't working for me.

Assuming the following simplified setup (a contact has multiple phone numbers):

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; }
}

I'd love to end up with something that returns a Contact with multiple Phone objects. That way, if I had 2 contacts, with 2 phones each, my SQL would return a join of those as a result set with 4 total rows. Then Dapper would pop out 2 contact objects with two phones each.

Here is the SQL in the stored procedure:

SELECT *
FROM Contacts
    LEFT OUTER JOIN Phones ON Phones.ReferenceId=Contacts.ReferenceId
WHERE clientid=1

I tried this, but ended up with 4 Tuples (which is OK, but not what I was hoping for... it just means I still have to re-normalize the result):

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);

and when I try another method (below), I get an exception of "Unable to cast object of type 'System.Int32' to type '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);

Am I just doing something wrong? It seems just like the posts/owner example, except that I'm going from the parent to the child instead of the child to the parent.

Thanks in advance

multi-mapping dapper
9 Answers

Once we decided to move our DataAccessLayer to stored procedures, and these procedures are often return multiple linked results (example below).

Well, my approach is almost the same, but maybe little bit more comfortable.

This is how your code may look like:

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();
}

Let's break it down...

Extension:

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 );
    }
}

Mapper:

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 );
}

That's all, but if you wanna do quick test, here is models and procedure for you:

Models:

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
user_85269570

use this:

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();
        }

took from: Managing relationShips

user_112417280
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