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Conversion failed when using User Defined Table Types #424
Description
Issue Summary
When using a User Defined Table Type it appears to write the value to the wrong column, resulting in a database conversion error. Using the SQL profiler I can see this error occurs before executing the SQL and only when the @parameter has one or more items. If it is empty or removed the command executes successfully.
Error
System.Data.SqlClient.SqlException: 'Conversion failed when converting the nvarchar value 'TestName' to data type int.
The statement has been terminated.'
To Reproduce
Possibly share SQL Schema, snippets of data, and how you call it in F#.
Sample to reproduce the behavior:
Table and Table Type
Create Table [TestTable] (
[C1] UniqueIdentifier Not Null,
[C2] UniqueIdentifier Not Null,
[C3] UniqueIdentifier Not Null,
[C4] NVarChar(100) Not Null,
[C5] NVarChar(100) Not Null,
[C6] NVarChar(100) Null,
[C7] NVarChar(1000) Not Null,
[C8] Int Not Null,
[C9] VarChar(10) Not Null,
[C10] UniqueIdentifier Not Null,
[C11] UniqueIdentifier Not Null,
Constraint [PK_Id] Primary Key Clustered([C1], [C2], [C3])
);
Create Type [dbo].[TestTableItem] AS Table(
[C3] UniqueIdentifier Not Null,
[C5] NVarChar(100) Not Null,
[C6] NVarChar(100) Null,
[C7] NVarChar(1000) Not Null,
[C8] Int Not Null,
[C9] VarChar(10) Not Null,
[C10] UniqueIdentifier Not Null
);
SqlCommandProvider
type AddSqlCommand = SqlCommandProvider<"
Insert [TestTable]
(
[C1],
[C2],
[C11],
[C4],
[C2],
[C5],
[C6],
[C7],
[C8],
[C9],
[C10]
)
Select
@C1,
@C2,
@C11,
@C4,
x.[C3],
x.[C5],
x.[C6],
x.[C7],
x.[C8],
x.[C9],
x.[C10]
From @C12 x;
" , staticConnectionString, TableVarMapping = "@C12=TestTableItem">
Usage
use cmd = new AddSqlCommand(connection, transaction = transaction)
let items =
[
AddSqlCommand.TestTableItem(
C3 = Guid.NewGuid(),
C5 = "TestName",
C6 = "C6",
C7 = "C7",
C8 = 1,
C9 = "C9",
C10 = Guid.NewGuid()
)
]
return!
cmd.AsyncExecute(
C1 = Guid.NewGuid(),
C2 = Guid.NewGuid(),
C4 = "C4 Name",
C11 = Guid.NewGuid(),
C12 = items
)
Expected behavior
The query should successfully insert a new row.
What you can do
- I am willing to contribute a PR with a unit test showcasing the issue
- I am willing to test the bug fix before next release
Activity
test attempting to reproduce issue fsprojects#424
smoothdeveloper commentedon Dec 3, 2022
@daniellittledev I've tried to reproduce the issue in #425 but the added test doesn't throw a SqlException, do you mind trying it out and adjust the test accordingly to reproduce your issue?
github-actions commentedon Mar 13, 2026
🤖 This is an automated response from Repo Assist.
Looking at the reproduction case, there appears to be a duplicate column name in the INSERT target list that might be causing the conversion error. In the sample SQL:
Insert [TestTable]( [C1], [C2], [C11], [C4], [C2], ← duplicate! [C3] was likely intended here [C5], ...Column
[C2]appears twice at positions 2 and 5, and[C3]is missing entirely. When SQL Server evaluates this with the UDTT values from@C12, position 5 of the VALUES (x.[C5], which isNVarChar(100)) is mapped against the wrong target column due to the duplicate. The resulting positional mismatch can cause the type conversion error you're seeing.To investigate: replace the second
[C2]in your INSERT column list with[C3]— this would align the UDTT column values with the correct target columns.Separately, on the library side: I traced through how
SqlMetaDataentries are generated for UDTT columns (inDesignTime.fsCreateUDTT) and column ordering there looks correct — columns are fetched fromsys.columnsordered bycolumn_id, and the constructor parameter order matches theSqlMetaDataarray order. So I don't believe the library is reordering columns.@daniellittledev— if the fix above resolves the issue, feel free to close. If you're seeing the conversion error even with a correct (non-duplicate) column list, please share the updated repro so the maintainer can investigate further with the test in PR #425.