Is it possible to do paging with JoinSqlBuilder? - servicestack

Question

I have a pretty normal join that I create via JoinSqlBuilder
var joinSqlBuilder = new JoinSqlBuilder<ProductWithManufacturer, Product>()
.Join<Product, Manufacturer>(sourceColumn: p => p.ManufacturerId,
destinationColumn: mf => mf.Id,
sourceTableColumnSelection: p => new { ProductId = p.Id, ProductName = p.Name },
destinationTableColumnSelection: m => new { ManufacturerId = m.Id, ManufacturerName = m.Name })
Of course, the join created by this could potentially return a lot of rows, so I want to use paging - preferably on the server-side. However, I cannot find anything in the JoinSqlBuilder which would let me do this? Am I missing something or does JoinSqlBuilder not have support for this (yet)?

Answer 1

If you aren't using MS SQL Server I think the following will work.
var sql = joinSqlBuilder.ToSql();
var data = this.Select<ProductWithManufacturer>(
q => q.Select(sql)
.Limit(skip,rows)
);
If you are working with MS SQL Server, it will most likely blow up on you. I am working to merge a more elegant solution similar to this into JoinSqlBuilder. The following is a quick and dirty method to accomplish what you want.
I created the following extension class:
public static class Extension
{
private static string ToSqlWithPaging<TResult, TTarget>(
this JoinSqlBuilder<TResult, TTarget> bldr,
string orderColumnName,
int limit,
int skip)
{
var sql = bldr.ToSql();
return string.Format(#"
SELECT * FROM (
SELECT ROW_NUMBER() OVER (ORDER BY [{0}]) As RowNum, *
FROM (
{1}
)as InnerResult
)as RowConstrainedResult
WHERE RowNum > {2} AND RowNum <= {3}
", orderColumnName, sql, skip, skip + limit);
}
public static string ToSqlWithPaging<TResult, TTarget>(
this JoinSqlBuilder<TResult, TTarget> bldr,
Expression<Func<TResult, object>> orderSelector,
int limit,
int skip)
{
var member = orderSelector.Body as MemberExpression;
if (member == null)
throw new ArgumentException(
"TResult selector refers to a non member."
);
var propInfo = member.Member as PropertyInfo;
if (propInfo == null)
throw new ArgumentException(
"TResult selector refers to a field, it must be a property."
);
var orderSelectorName = propInfo.Name;
return ToSqlWithPaging(bldr, orderSelectorName, limit, skip);
}
}
It is applied as follows:
List<Entity> GetAllEntities(int limit, int skip)
{
var bldr = GetJoinSqlBuilderFor<Entity>();
var sql = bldr.ToSqlWithPaging(
entity => entity.Id,
limit,
skip);
return this.Db.Select<Entity>(sql);
}