Error scanning into a var of type []sql.NullString

[taylorsilva]

I have a query that uses array_agg() in one of the columns.
When I try and scan the result into a var of type []sql.NullString I get this error:

sql: Scan error on column index 3, name "passed": cannot convert to sql.Scanner: cannot find registered type for *[]sql.NullString

Are slices of the sql types not supported by pgx? I got the same error with a []sql.NullInt64 var as well in another part of my codebase.

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More info:

• The data being passed into array_agg() is TEXT
• I'm migrating from lib/pq to pgx. pq had no issue with scanning into []sql.NullString
• I've seen in other places pgx have no issue scanning into a var of type sql.NullString. It's only been when I have slices of any of the database/sql types that this error comes up

[ousloob]

@taylorsilva
The issue arises because pgx does not support scanning directly into slices of sql.NullString (or other database/sql nullable types). However, pgx does support scanning into Go slices of native types like []string.

To work around this, you can use []string instead (if you don't need to differentiate NULL values).
Use pgtype.TextArray from pgx's pgtype package if you need more control over NULL values.

Hope this helps! 🙂

[taylorsilva]

Thanks for clarifying!

I ended up wrapping my array_agg() in an array_remove, so I had this in my query in the end:

array_remove(array_agg(...), NULL)

Then I was able to scan the result into a var of type []string. If I didn't have the array_remove() in there then I could only scan into an []*string, which makes sense given your answer.