Postgres connector

Read Postgres tables via PgTableSource and write with declare_table_target() — automatic schema inference, pgvector index management (ivfflat / hnsw), custom type overrides, and SQL attachments for triggers and indexes.

Version: v 1.0.0-alpha48
Last reviewed: Apr 20, 2026

The postgres connector provides utilities for reading rows from and writing rows to PostgreSQL databases, with built-in support for pgvector.

python

from cocoindex.connectors import postgres

Dependencies

This connector requires additional dependencies. Install with:

bash

pip install cocoindex[postgres]

Connection setup

Create an asyncpg connection pool directly:

python

import asyncpg

pool = await asyncpg.create_pool("postgresql://user:pass@localhost/dbname")

The connector handles pgvector extension setup automatically when a table uses vector columns — no special pool initialization is needed.

As source

Use PgTableSource to read rows from a PostgreSQL table. It returns a RowFetcher that supports both synchronous and asynchronous iteration.

PgTableSource

python

class PgTableSource(Generic[RowT]):
    def __init__(
        self,
        pool: asyncpg.Pool,
        *,
        table_name: str,
        columns: Sequence[str] | None = None,
        pg_schema_name: str | None = None,
        row_type: type[RowT] | None = None,
        row_factory: Callable[[dict[str, Any]], RowT] | None = None,
    ) -> None

    def fetch_rows(self) -> RowFetcher[RowT]

Parameters:

pool — An asyncpg connection pool.
table_name — Name of the table to read from.
columns — List of column names to select. If omitted with row_type, uses the record’s field names. If omitted without row_type, uses SELECT *.
pg_schema_name — Optional PostgreSQL schema name (defaults to "public").
row_type — Optional record type (dataclass, NamedTuple, or Pydantic model) for automatic row conversion. When provided, columns (if specified) must be a subset of the record’s fields.
row_factory — Optional callable to transform each row dict. Mutually exclusive with row_type.

Row mapping

By default, rows are returned as dict[str, Any], with PostgreSQL types converted to Python types using asyncpg’s type conversion. You can configure automatic conversion to custom types using row_type or row_factory.

Using `row_type`

Pass a record type (dataclass, NamedTuple, or Pydantic model) to automatically convert rows. When columns is omitted, the record’s field names are used:

python

from dataclasses import dataclass

@dataclass
class Product:
    id: int
    name: str
    price: float

source = postgres.PgTableSource(
    pool,
    table_name="products",
    row_type=Product,  # columns inferred as ["id", "name", "price"]
)

Using `row_factory`

For custom transformations, pass a callable:

python

source = postgres.PgTableSource(
    pool,
    table_name="products",
    columns=["id", "name", "price"],
    row_factory=lambda row: (row["name"], row["price"] * 1.1),  # Add 10% markup
)

Iterating rows

fetch_rows() returns a RowFetcher that supports both sync and async iteration:

python

# Synchronous iteration
for row in source.fetch_rows():
    print(row.name, row.price)

# Asynchronous iteration (streams rows using a cursor)
async for row in source.fetch_rows():
    print(row.name, row.price)

Example

python

import cocoindex as coco
from cocoindex.connectors import postgres

@dataclass
class SourceProduct:
    product_id: str
    name: str
    description: str

@coco.fn
async def app_main(pool: asyncpg.Pool) -> None:
    source = postgres.PgTableSource(
        pool,
        table_name="products",
        row_type=SourceProduct,
    )

    async for product in source.fetch_rows():
        coco.mount(
            coco.component_subpath("product", product.product_id),
            process_product,
            product,
        )

As target

The postgres connector provides target state APIs for writing rows to tables. With it, CocoIndex tracks what rows should exist and automatically handles upserts and deletions.

Declaring target states

Setting up a connection

Create a ContextKey[asyncpg.Pool] to identify your connection pool, then provide the pool directly in your lifespan:

Note

The key name is load-bearing across runs — it’s the stable identity CocoIndex uses to track managed rows. See ContextKey as stable identity before renaming.

python

import asyncpg
import cocoindex as coco

PG_DB = coco.ContextKey[asyncpg.Pool]("my_db")

@coco.lifespan
async def coco_lifespan(builder: coco.EnvironmentBuilder) -> AsyncIterator[None]:
    async with await asyncpg.create_pool(DATABASE_URL) as pool:
        builder.provide(PG_DB, pool)
        yield

Tables (parent state)

Declares a table as a target state. Returns a TableTarget for declaring rows.

python

def declare_table_target(
    db: ContextKey[asyncpg.Pool],
    table_name: str,
    table_schema: TableSchema[RowT],
    *,
    pg_schema_name: str | None = None,
    managed_by: Literal["system", "user"] = "system",
) -> TableTarget[RowT, coco.PendingS]

Parameters:

db — A ContextKey[asyncpg.Pool] identifying the connection pool to use.
table_name — Name of the table.
table_schema — Schema definition including columns and primary key (see Table Schema).
pg_schema_name — Optional PostgreSQL schema name (defaults to "public").
managed_by — Whether CocoIndex manages the table lifecycle ("system") or assumes it exists ("user").

Returns: A pending TableTarget. Use the convenience wrapper await postgres.mount_table_target(PG_DB, table_name, table_schema) to resolve.

Rows (child states)

Once a TableTarget is resolved, declare rows to be upserted:

python

def TableTarget.declare_row(
    self,
    *,
    row: RowT,
) -> None

Parameters:

row — A row object (dict, dataclass, NamedTuple, or Pydantic model). Must include all primary key columns.

Vector indexes (attachment)

Declare a pgvector index on a vector column of the table. CocoIndex tracks the index spec and automatically creates, recreates, or drops the index as needed.

python

def TableTarget.declare_vector_index(
    self,
    *,
    name: str | None = None,
    column: str,
    metric: Literal["cosine", "l2", "ip"] = "cosine",
    method: Literal["ivfflat", "hnsw"] = "ivfflat",
    lists: int | None = None,
    m: int | None = None,
    ef_construction: int | None = None,
) -> None

The actual PostgreSQL index is named {table_name}__vector__{name}.

Parameters:

name — Logical index name (defaults to column).
column — Column to index (must be a vector column).
metric — Distance metric: "cosine", "l2", or "ip" (inner product).
method — Index method: "ivfflat" or "hnsw".
lists — Number of lists (ivfflat only).
m — Maximum number of connections per layer (hnsw only).
ef_construction — Size of the dynamic candidate list for construction (hnsw only).

Example:

python

# Creates a PostgreSQL index named "products__vector__embedding"
table.declare_vector_index(
    column="embedding",
    metric="cosine",
    method="hnsw",
    m=16,
    ef_construction=64,
)

SQL command attachments

Declare an arbitrary SQL command that CocoIndex manages alongside the table. The setup SQL runs when the attachment is created or changed; the optional teardown SQL runs when the attachment is removed or before re-running setup on change.

python

def TableTarget.declare_sql_command_attachment(
    self,
    *,
    name: str,
    setup_sql: str,
    teardown_sql: str | None = None,
) -> None

Parameters:

name — Stable identifier for the attachment.
setup_sql — SQL to execute on creation or change.
teardown_sql — SQL to execute on removal or before re-running setup (optional). If omitted, no cleanup is performed when the attachment is removed.

Example:

python

table.declare_sql_command_attachment(
    name="content_fts_idx",
    setup_sql='CREATE INDEX "content_fts" ON "products" USING gin (to_tsvector(\'english\', "description"))',
    teardown_sql='DROP INDEX IF EXISTS "content_fts"',
)

Table schema: from Python class

Define the table structure using a Python class (dataclass, NamedTuple, or Pydantic model):

python

@classmethod
async def TableSchema.from_class(
    cls,
    record_type: type[RowT],
    primary_key: list[str],
    *,
    column_overrides: dict[str, PgType | VectorSchemaProvider] | None = None,
) -> TableSchema[RowT]

Parameters:

record_type — A record type whose fields define table columns.
primary_key — List of column names forming the primary key.
column_overrides — Optional per-column overrides for type mapping or vector configuration.

Example:

python

@dataclass
class OutputProduct:
    category: str
    name: str
    price: float
    embedding: Annotated[NDArray, embedder]

schema = await postgres.TableSchema.from_class(
    OutputProduct,
    primary_key=["category", "name"],
)

Python types are automatically mapped to PostgreSQL types:

Python Type	PostgreSQL Type
`bool`	`boolean`
`int`	`bigint`
`float`	`double precision`
`decimal.Decimal`	`numeric`
`str`	`text`
`bytes`	`bytea`
`uuid.UUID`	`uuid`
`datetime.date`	`date`
`datetime.time`	`time with time zone`
`datetime.datetime`	`timestamp with time zone`
`datetime.timedelta`	`interval`
`list`, `dict`, nested structs	`jsonb`
`NDArray` (with vector schema)	`vector(n)` or `halfvec(n)`

To override the default mapping, provide a PgType or VectorSchemaProvider via:

Type annotation — using typing.Annotated on the field
column_overrides — passing overrides when constructing TableSchema

PgType

Use PgType to specify a custom PostgreSQL type:

python

from typing import Annotated
from cocoindex.connectors.postgres import PgType

@dataclass
class MyRow:
    id: Annotated[int, PgType("integer")]           # instead of bigint
    value: Annotated[float, PgType("real")]         # instead of double precision
    created_at: Annotated[datetime.datetime, PgType("timestamp")]  # without timezone

Or via column_overrides:

python

schema = postgres.TableSchema(
    MyRow,
    primary_key=["id"],
    column_overrides={
        "created_at": postgres.PgType("timestamp"),
    },
)

VectorSchemaProvider

For NDArray fields, a VectorSchemaProvider annotation specifies the vector dimension and dtype. The connector has built-in pgvector support and automatically creates the extension when needed. See Vector Schema for the full list of annotation options (ContextKey, embedder instance, or explicit VectorSchema).

Table schema: explicit column definitions

Define columns directly using ColumnDef:

python

def TableSchema.__init__(
    self,
    columns: dict[str, ColumnDef],
    primary_key: list[str],
) -> None

Example:

python

schema = postgres.TableSchema(
    {
        "category": postgres.ColumnDef(type="text", nullable=False),
        "name": postgres.ColumnDef(type="text", nullable=False),
        "price": postgres.ColumnDef(type="numeric"),
        "embedding": postgres.ColumnDef(type="vector(384)"),
    },
    primary_key=["category", "name"],
)

Example

python

import asyncpg
import cocoindex as coco
from cocoindex.connectors import postgres

DATABASE_URL = "postgresql://localhost/mydb"

PG_DB = coco.ContextKey[asyncpg.Pool]("main_db")

@dataclass
class OutputProduct:
    category: str
    name: str
    description: str
    embedding: Annotated[NDArray, embedder]

@coco.lifespan
async def coco_lifespan(builder: coco.EnvironmentBuilder) -> AsyncIterator[None]:
    async with await asyncpg.create_pool(DATABASE_URL) as pool:
        builder.provide(PG_DB, pool)
        yield

@coco.fn
async def app_main() -> None:
    # Declare table target state
    table = await postgres.mount_table_target(
        PG_DB,
        "products",
        await postgres.TableSchema.from_class(
            OutputProduct,
            primary_key=["category", "name"],
        ),
    )

    # Declare rows
    for product in products:
        table.declare_row(row=product)

    # Declare a vector index on the embedding column
    table.declare_vector_index(
        column="embedding",
        metric="cosine",
        method="hnsw",
    )

Postgres connector

Connection setup

As source

PgTableSource

Row mapping

Using row_type

Using row_factory

Iterating rows

Example

As target

Declaring target states

Setting up a connection

Tables (parent state)

Rows (child states)

Vector indexes (attachment)

SQL command attachments

Table schema: from Python class

PgType

VectorSchemaProvider

Table schema: explicit column definitions

Example

Using `row_type`

Using `row_factory`