Export SQL for a migration

[olirice]

Vecs does not currently interop well with migrations.

Provide a function that exports a SQL snippet that can be used to setup a migration

Example

docs = vx.create_collection(...)

docs.export_migration()
# Returns: "create table vecs.docs ......"

[TemaDeveloper]

Hi @olirice — happy to take this. Proposed API per the issue body:

def export_migration(
    self,
    *,
    include_extension: bool = True,
    include_schema: bool = True,
    if_not_exists: bool = True,
) -> str:

Returns the DDL needed to recreate the collection's table and metadata index, suitable for pasting into Alembic / sqitch / raw migration files. Sample output for create_collection(name="docs", dimension=3):

create extension if not exists vector;
create schema if not exists vecs;
CREATE TABLE IF NOT EXISTS vecs.docs (
    id VARCHAR NOT NULL,
    vec VECTOR(3) NOT NULL,
    metadata JSONB DEFAULT '{}'::jsonb NOT NULL,
    PRIMARY KEY (id)
);
create index if not exists ix_meta_docs
  on vecs."docs" using gin (metadata jsonb_path_ops);

Two design choices I'd like to confirm before I open a PR:

1. Index naming. _create currently uses ix_meta_<uuid> for the metadata GIN index to avoid collisions. For a migration this needs to be deterministic, so I'd switch to ix_meta_<collection_name>. Sound right, or would you prefer the caller pass an explicit name?
2. Vector indexes excluded. create_index picks n_lists from the current row count and chooses HNSW vs IVFFlat from the live pgvector version, so I'd leave it out of export_migration. Users would still call collection.create_index() after data is loaded. Agree, or do you want a separate export_index_migration(method=..., n_lists=...)?

I have an implementation + tests ready locally; happy to push as soon as you ack the approach. PR will follow the Conventional Commits format (feat(collection): add export_migration for SQL DDL export) and link back to this issue.