Is it possible to create table-valued *methods* in a SQL CLR user-defined type?

Question

I have a CLR UDT that would benefit greatly from table-valued methods, ala xml.nodes():

-- nodes() example, for reference:
declare @xml xml = '<id>1</id><id>2</id><id>5</id><id>10</id>'
select c.value('.','int') as id from @xml.nodes('/id') t (c)

I want something similar for my UDT:

-- would return tuples (1, 4), (1, 5), (1, 6)....(1, 20)
declare @udt dbo.FancyType = '1.4:20'
select * from @udt.AsTable() t (c)

Does anyone have any experience w/ this? Any help would be greatly appreciated. I've tried a few things and they've all failed. I've looked for documentation and examples and found none.

Yes, I know I could create table-valued UDFs that take my UDT as a parameter, but I was rather hoping to bundle everything inside a single type, OO-style.

EDIT

Russell Hart found the documentation states that table-valued methods are not supported, and fixed my syntax to produce the expected runtime error (see below).

In VS2010, after creating a new UDT, I added this at the end of the struct definition:

[SqlMethod(FillRowMethodName = "GetTable_FillRow", TableDefinition = "Id INT")]
public IEnumerable GetTable()
{
    ArrayList resultCollection = new ArrayList();
    resultCollection.Add(1);
    resultCollection.Add(2);
    resultCollection.Add(3);
    return resultCollection;
}

public static void GetTable_FillRow(object tableResultObj, out SqlInt32 Id)
{
    Id = (int)tableResultObj;
}

This builds and deploys successfully. But then in SSMS, we get a runtime error as expected (if not word-for-word):

-- needed to alias the column in the SELECT clause, rather than after the table alias.
declare @this dbo.tvm_example = ''
select t.[Id] as [ID] from @this.GetTable() as [t]

Msg 2715, Level 16, State 3, Line 2
Column, parameter, or variable #1: Cannot find data type dbo.tvm_example.
Parameter or variable '@this' has an invalid data type.

So, it seems it is not possible after all. And even if were possible, it probably wouldn't be wise, given the restrictions on altering CLR objects in SQL Server.

That said, if anyone knows a hack to get around this particular limitation, I'll raise a new bounty accordingly.

Answer 1

You have aliased the table but not the columns. Try,

declare @this dbo.tvm_example = ''
select t.[Id] as [ID] from @this.GetTable() as [t]

According to the documentation, http://msdn.microsoft.com/en-us/library/ms131069(v=SQL.100).aspx#Y4739, this should fail on another runtime error regarding incorrect type.

The SqlMethodAttribute class inherits from the SqlFunctionAttribute class, so SqlMethodAttribute inherits the FillRowMethodName and TableDefinition fields from SqlFunctionAttribute. This implies that it is possible to write a table-valued method, which is not the case. The method compiles and the assembly deploys, but an error about the IEnumerable return type is raised at runtime with the following message: "Method, property, or field '' in class '' in assembly '' has invalid return type."

They may be avoiding supporting such a method. If you alter the assembly with method updates this can cause problems to the data in UDT columns. An appropriate solution is to have a minimal UDT, then a seperate class of methods to accompany it. This will ensure flexibility and fully featured methods.

xml nodes method will not change so it is not subject to the same implemetation limitations.

Hope this helps Peter and good luck.