Add support for SQL Variant fields

[akilude]

Adds support for sql_variant field which causes the following error:
"ODBC SQL type -150 is not yet supported. column-index=0 type=-150', 'HY106'"

This commit converts these fields output to a string

[dauinsight]

Hi @akilude, thank you for contributing. Could you provide a test case for this feature?

[akilude]

Hi @akilude, thank you for contributing. Could you provide a test case for this feature?

Hi,

Sure, will add it early next week.

[akilude]

@dauinsight, could you please give me a couple of pointers on how to provide a test case for this.

This feature will mainly be used with existing external databases. When we have an external mssql database with a field of type "sql_variant", this PR will convert the data to string and return it to django.

I think there are only test cases for database created with django?

[dauinsight]

@dauinsight, could you please give me a couple of pointers on how to provide a test case for this.

This feature will mainly be used with existing external databases. When we have an external mssql database with a field of type "sql_variant", this PR will convert the data to string and return it to django.

I think there are only test cases for database created with django?

Good question, we can use Django's RunSQL function to make a custom migration with a sql_variant type:

https://docs.djangoproject.com/en/5.0/ref/migration-operations/#runsql

[dauinsight]

Hi @akilude, an example test might look like:

        connection = connections['default']
        with connection.cursor() as cursor:
            cursor.execute("CREATE TABLE tableA(colA sql_variant, colB INT)")
            cursor.execute("INSERT INTO tableA values (CAST(46279.1 as decimal(8,2)), 1689)")
            cursor.execute("SELECT colA FROM tableA WHERE colB=1689")

            rows = cursor.fetchall()

[akilude]

Thanks @dauinsight, bit busy with work, will add it in a day or two.

[akilude]

@dauinsight, apologies for the delay, have added the test case.

Please let me know if any changes are needed. Thanks.

[dauinsight]

I'm not too familiar with the sql_variant type but it looks like this method of decoding is likely to result in incorrect data.

Since sql_variant can contain multiple types, unpacking the data in a reliable manner seems difficult... We might be better off doing an explicit CAST in sql.

[akilude]

@dauinsight We can find the base type of the field https://learn.microsoft.com/en-us/sql/t-sql/functions/sql-variant-property-transact-sql?view=sql-server-ver16

in the converter function, shall we convert whatever type to string and return.

[akilude]

@dauinsight, please let me know the best way to proceed. Thanks.