Supabase database errorSupabase: “null value in column violates not-null constraint” (23502)

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Why the column is empty, and the fix

1. 01

   The insert doesn’t send the column

   “If no default value is declared explicitly, the default value is the null value.” PostgreSQL docs, Default values

   A column left out of the insert gets its default. With no default, that is null, and a NOT NULL column refuses it.

2. 02

   user_id should come from the session

   Let the database fill user_id from the signed-in user, so the client can’t forget it or send someone else’s. Keep an RLS policy that checks it. A default only applies when the column is left out: an explicit null still fails, and so does an insert from a signed-out client, because auth.uid() is null. In supabase-js bulk inserts, missing fields become null unless you pass defaultToNull: false.

   alter table public.todos
     alter column user_id set default auth.uid();
   
   -- the client can now insert without user_id
   -- supabase.from('todos').insert({ title: 'Buy milk' })

3. 03

   A sign-up trigger writes a missing field

   A trigger on auth.users that copies raw_user_meta_data into a profile writes null when sign-up didn’t send that field. Sign-up then fails with “Database error saving new user”. Use coalesce with a fallback, or allow null in that column.

   insert into public.profiles (id, full_name)
   values (new.id, coalesce(new.raw_user_meta_data->>'full_name', ''));

4. 04

   An update sets the column to null

   “A not-null constraint simply specifies that a column must not assume the null value.” PostgreSQL docs, Constraints (not-null)

   An update or upsert that sends the column as null, for example from an empty form field, fails the same way. Leave the field out of the update when it has no value.

5. 05

   Making an old column required

   “SET NOT NULL may only be applied to a column provided none of the records in the table contain a NULL value for the column.” PostgreSQL docs, ALTER TABLE

   Adding NOT NULL to a column that already has empty rows fails. Fill them first, then add the constraint.

   update public.todos set status = 'open' where status is null;
   alter table public.todos alter column status set not null;

Checked against the vendor’s docs on November 9, 2026: PostgreSQL docs: Constraints (not-null); PostgreSQL docs: Default values; PostgreSQL docs: ALTER TABLE.

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