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This is a beta feature available in versions 0.22.0 and above.
Postgres allows a maximum of 32 columns in an index definition, but because ParadeDB benefits from pushing filters and ranking signals into the BM25 index this can become a limitation. To index more than 32 columns in a single BM25 index, wrap columns in a ROW() expression cast to a composite type. ParadeDB will unpack the composite type and index each field individually.

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Creating a Composite Type

First, define a composite type whose field names and types match the columns you want to index: 
CREATE TYPE item_fields AS (description TEXT, category TEXT, rating INTEGER);
Then reference the columns in a ROW() expression cast to the composite type: 
CREATE INDEX search_idx ON mock_items
USING bm25 (id, (ROW(description, category, rating)::item_fields))
WITH (key_field='id');
Each field in the composite type is indexed as if it were a standalone column. Queries use the field names directly with the standard operators: 
SELECT description, category FROM mock_items
WHERE description &&& 'running shoes';

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Configuring Tokenizers

Fields in the composite type can use tokenizers and token filters by specifying them as the field type: 
CREATE TYPE item_fields AS (
    description pdb.simple('stemmer=english'),
    category pdb.literal,
    in_stock BOOLEAN
);

CREATE INDEX search_idx ON mock_items
USING bm25 (id, (ROW(description, category, in_stock)::item_fields))
WITH (key_field='id');

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Constraints

The following are not supported and will produce an error:
  • Anonymous ROW expressions: ROW(a, b) without a type cast is not allowed. Always cast to a named composite type.
  • Nested composites: A composite type cannot contain another composite type as a field.
  • Duplicate field names: Field names must be unique across all composite types and regular columns in the index.