使用AliasToBean转换器在对象属性的映射实体列表到逗号分隔的DTO字符串属性的Nhibernate查询

Question

I want to use query over to map a List of Object To a Flat Comma-Separated String Using Alias To Bean Transformer.

This Is My Query Over:

 var query = QueryOver<WorkList>();
 query.SelectList(list => list
   .Select(p => p.ID).WithAlias(() => dto.ID)
   .Select(p => p.Name).WithAlias(() => dto.Name)
   .Select( p => p.Commodities).WithAlias(() => dto.CommodityList)

 return query;

The Commodities in the select clause is a List of Commodity Object. Now I want to Map this to a Comma-Separated String. All my code is working fine but I want to transform this to a Comma-Separated String.

I am Using AliasToBean Transformer where I return a Flat Dto Object.

Answer 1

On top of my head: First, you should create a user-defined function in SQL Server like eg this:

create function listProductCommodities(@productId INT)
returns varchar(8000) 
as 
begin
    declare @result varchar(8000)
    declare @name varchar(8000)

    set @result = null

    declare com_cursor cursor for
    select name
    from commodities
    where userid = @productId

    open com_cursor

    fetch next from com_cursor into @name

    while @@FETCH_STATUS = 0 
    begin
        if @result is null
            set @result = @name
        else
            set @result = @result + ',' + @name

        fetch next from com_cursor into @name
    end

    close com_cursor

    deallocate com_cursor

    return @result
end

Then you should use this function in a subquery:

WorkList workList = null;
<your dto class name> dto = null;
Commodity commodity = null;

var subquery = QueryOver.Of(() => commodity)
    .Where(() => commodity.ProductId == workList.ID) // instead of ProductId put your foreign key property name
    .Select(Projections.SqlFunction("listProductCommodities",
        NHibernateUtil.String,
        Projections.Distinct(Projections.Property(() => commodity.Name))); //instead of name put your text field

var query = Session.QueryOver(() => workList)
    .SelectList(list => list
        .Select(p => p.ID).WithAlias(() => dto.ID)
        .Select(p => p.Name).WithAlias(() => dto.Name)
        .SelectSubQuery(subquery).WithAlias(() => dto.CommodityList))
    .TransformUsing(Transformers.AliasToBean<your dto class name>())
    .List<your dto class name>();

I made some assumptions about your table/property/class names so you should adjust it to your needs.

But main idea is to create function in SQL Server and then map this function to subquery via NHibernate's SqlFunction . Other database may have built-in "list" function but SQL Server doesn't - so you should workaround it. My implementation of listProductCommodities isn't very good as it uses cursor. However, on small amounts of data this will work.

But there's another option - you can issue another sql query to get array of commodity names, build string from that array via string.join and then assign DTO's property manually.