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1429b54
Chore: Adjust `test.py`
amotl Apr 2, 2025
8031f7c
CrateDB: Hello, World!
amotl Apr 2, 2025
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3 changes: 2 additions & 1 deletion .gitignore
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
**/.DS_Store
.env
.idea
.venv/
__pycache__/
__pycache__/
44 changes: 44 additions & 0 deletions README-CRATEDB.md
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@@ -0,0 +1,44 @@
# CrateDB Model Context Protocol Server

## About

This CrateDB MCP Server is based on the PostgreSQL Model Context Protocol (PG-MCP) Server.
[pg-mcp] uses [asyncpg], so it can also be used with CrateDB.

`server/resources/schema.py` received a few adjustments to compensate for
missing metadata features of CrateDB, nothing serious.

## Usage

Start CrateDB.
```shell
docker run --rm \
--name=cratedb --publish=4200:4200 --publish=5432:5432 \
--env=CRATE_HEAP_SIZE=2g crate/crate:nightly \
-Cdiscovery.type=single-node
```

Initialize Python environment.
```shell
git clone https://github.com/crate-workbench/pg-mcp --branch=cratedb
cd pg-mcp
uv venv --python 3.13 --seed .venv
uv sync --frozen
```

Run MCP server and test program.
```shell
uv run -m server.app
uv run test.py "postgresql://crate@localhost/doc"
```

Run example Claude session (untested).
```shell
export DATABASE_URL=postgresql://crate@localhost
export ANTHROPIC_API_KEY=...
uv run -m client.claude_cli "Give me 5 Austria mountains (querying specific tables, like sys.summits)"
```


[asyncpg]: https://pypi.org/project/asyncpg
[pg-mcp]: https://github.com/stuzero/pg-mcp
112 changes: 22 additions & 90 deletions server/resources/schema.py
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Expand Up @@ -18,8 +18,7 @@ async def db_info(conn_id: str):
# Get all non-system schemas
schemas_query = """
SELECT
schema_name,
obj_description(pg_namespace.oid) as description
schema_name
FROM information_schema.schemata
JOIN pg_namespace ON pg_namespace.nspname = schema_name
WHERE
Expand All @@ -45,9 +44,7 @@ async def db_info(conn_id: str):
# Get all tables in the schema
tables_query = """
SELECT
t.table_name,
obj_description(format('"%s"."%s"', t.table_schema, t.table_name)::regclass::oid) as description,
pg_stat_get_tuples_inserted(format('"%s"."%s"', t.table_schema, t.table_name)::regclass::oid) as row_count
t.table_name
FROM information_schema.tables t
WHERE
t.table_schema = $1
Expand Down Expand Up @@ -76,16 +73,15 @@ async def db_info(conn_id: str):
c.column_name,
c.data_type,
c.is_nullable,
c.column_default,
col_description(format('"%s"."%s"', c.table_schema, c.table_name)::regclass::oid, c.ordinal_position) as description
c.column_default
FROM information_schema.columns c
WHERE
c.table_schema = $1 AND
c.table_name = $2
ORDER BY c.ordinal_position
"""
columns = await execute_query(columns_query, conn_id, [schema_name, table_name])

# Get constraints for this table to identify primary keys, etc.
constraints_query = """
SELECT
Expand All @@ -97,18 +93,15 @@ async def db_info(conn_id: str):
WHEN c.contype = 'f' THEN 'FOREIGN KEY'
WHEN c.contype = 'c' THEN 'CHECK'
ELSE 'OTHER'
END as constraint_type_desc,
ARRAY_AGG(col.attname ORDER BY u.attposition) as column_names
END as constraint_type_desc
FROM
pg_constraint c
JOIN
pg_namespace n ON n.oid = c.connamespace
JOIN
pg_class t ON t.oid = c.conrelid
LEFT JOIN
LATERAL unnest(c.conkey) WITH ORDINALITY AS u(attnum, attposition) ON TRUE
LEFT JOIN
pg_attribute col ON col.attrelid = t.oid AND col.attnum = u.attnum
pg_attribute col ON col.attrelid = t.oid
WHERE
n.nspname = $1
AND t.relname = $2
Expand All @@ -118,7 +111,7 @@ async def db_info(conn_id: str):
c.contype, c.conname
"""
constraints = await execute_query(constraints_query, conn_id, [schema_name, table_name])

# Process columns and add constraint information
for column in columns:
column_name = column['column_name']
Expand All @@ -128,56 +121,22 @@ async def db_info(conn_id: str):
for constraint in constraints:
if column_name in constraint.get('column_names', []):
column_constraints.append(constraint['constraint_type_desc'])

# Add column info
column_info = {
"name": column_name,
"type": column['data_type'],
"nullable": column['is_nullable'] == 'YES',
"default": column['column_default'],
"description": column['description'],
"constraints": column_constraints
}

table_info["columns"].append(column_info)

# Process foreign key constraints
foreign_keys_query = """
SELECT
c.conname as constraint_name,
ARRAY_AGG(col.attname ORDER BY u.attposition) as column_names,
nr.nspname as referenced_schema,
ref_table.relname as referenced_table,
ARRAY_AGG(ref_col.attname ORDER BY u2.attposition) as referenced_columns
FROM
pg_constraint c
JOIN
pg_namespace n ON n.oid = c.connamespace
JOIN
pg_class t ON t.oid = c.conrelid
JOIN
pg_class ref_table ON ref_table.oid = c.confrelid
JOIN
pg_namespace nr ON nr.oid = ref_table.relnamespace
LEFT JOIN
LATERAL unnest(c.conkey) WITH ORDINALITY AS u(attnum, attposition) ON TRUE
LEFT JOIN
pg_attribute col ON col.attrelid = t.oid AND col.attnum = u.attnum
LEFT JOIN
LATERAL unnest(c.confkey) WITH ORDINALITY AS u2(attnum, attposition) ON TRUE
LEFT JOIN
pg_attribute ref_col ON ref_col.attrelid = c.confrelid AND ref_col.attnum = u2.attnum
WHERE
n.nspname = $1
AND t.relname = $2
AND c.contype = 'f'
GROUP BY
c.conname, nr.nspname, ref_table.relname
ORDER BY
c.conname
"""
foreign_keys = await execute_query(foreign_keys_query, conn_id, [schema_name, table_name])

# CrateDB does not provide foreign key constraints.
foreign_keys = []

for fk in foreign_keys:
fk_info = {
"name": fk['constraint_name'],
Expand All @@ -201,8 +160,7 @@ async def list_schemas(conn_id: str):
"""List all non-system schemas in the database."""
query = """
SELECT
schema_name,
obj_description(pg_namespace.oid) as description
schema_name
FROM information_schema.schemata
JOIN pg_namespace ON pg_namespace.nspname = schema_name
WHERE
Expand All @@ -217,9 +175,7 @@ async def list_schema_tables(conn_id: str, schema: str):
"""List all tables in a specific schema with their descriptions."""
query = """
SELECT
t.table_name,
obj_description(format('"%s"."%s"', t.table_schema, t.table_name)::regclass::oid) as description,
pg_stat_get_tuples_inserted(format('"%s"."%s"', t.table_schema, t.table_name)::regclass::oid) as total_rows
t.table_name
FROM information_schema.tables t
WHERE
t.table_schema = $1
Expand All @@ -236,8 +192,7 @@ async def get_table_columns(conn_id: str, schema: str, table: str):
c.column_name,
c.data_type,
c.is_nullable,
c.column_default,
col_description(format('"%s"."%s"', c.table_schema, c.table_name)::regclass::oid, c.ordinal_position) as description
c.column_default
FROM information_schema.columns c
WHERE
c.table_schema = $1 AND
Expand All @@ -252,10 +207,7 @@ async def get_table_indexes(conn_id: str, schema: str, table: str):
query = """
SELECT
i.relname as index_name,
pg_get_indexdef(i.oid) as index_definition,
obj_description(i.oid) as description,
am.amname as index_type,
ARRAY_AGG(a.attname ORDER BY k.i) as column_names,
ix.indisunique as is_unique,
ix.indisprimary as is_primary,
ix.indisexclusion as is_exclusion
Expand All @@ -270,9 +222,7 @@ async def get_table_indexes(conn_id: str, schema: str, table: str):
JOIN
pg_am am ON i.relam = am.oid
LEFT JOIN
LATERAL unnest(ix.indkey) WITH ORDINALITY AS k(attnum, i) ON TRUE
LEFT JOIN
pg_attribute a ON a.attrelid = t.oid AND a.attnum = k.attnum
pg_attribute a ON a.attrelid = t.oid
WHERE
n.nspname = $1
AND t.relname = $2
Expand All @@ -299,14 +249,11 @@ async def get_table_constraints(conn_id: str, schema: str, table: str):
WHEN c.contype = 'x' THEN 'EXCLUSION'
ELSE 'OTHER'
END as constraint_type_desc,
obj_description(c.oid) as description,
pg_get_constraintdef(c.oid) as definition,
CASE
WHEN c.contype = 'f' THEN
(SELECT nspname FROM pg_namespace WHERE oid = ref_table.relnamespace) || '.' || ref_table.relname
ELSE NULL
END as referenced_table,
ARRAY_AGG(col.attname ORDER BY u.attposition) as column_names
END as referenced_table
FROM
pg_constraint c
JOIN
Expand All @@ -316,9 +263,7 @@ async def get_table_constraints(conn_id: str, schema: str, table: str):
LEFT JOIN
pg_class ref_table ON ref_table.oid = c.confrelid
LEFT JOIN
LATERAL unnest(c.conkey) WITH ORDINALITY AS u(attnum, attposition) ON TRUE
LEFT JOIN
pg_attribute col ON col.attrelid = t.oid AND col.attnum = u.attnum
pg_attribute col ON col.attrelid = t.oid
WHERE
n.nspname = $1
AND t.relname = $2
Expand All @@ -335,8 +280,6 @@ async def get_index_details(conn_id: str, schema: str, table: str, index: str):
query = """
SELECT
i.relname as index_name,
pg_get_indexdef(i.oid) as index_definition,
obj_description(i.oid) as description,
am.amname as index_type,
ix.indisunique as is_unique,
ix.indisprimary as is_primary,
Expand All @@ -345,9 +288,7 @@ async def get_index_details(conn_id: str, schema: str, table: str, index: str):
ix.indisclustered as is_clustered,
ix.indisvalid as is_valid,
i.relpages as pages,
i.reltuples as rows,
ARRAY_AGG(a.attname ORDER BY k.i) as column_names,
ARRAY_AGG(pg_get_indexdef(i.oid, k.i, false) ORDER BY k.i) as column_expressions
i.reltuples as rows
FROM
pg_index ix
JOIN
Expand All @@ -359,9 +300,7 @@ async def get_index_details(conn_id: str, schema: str, table: str, index: str):
JOIN
pg_am am ON i.relam = am.oid
LEFT JOIN
LATERAL unnest(ix.indkey) WITH ORDINALITY AS k(attnum, i) ON TRUE
LEFT JOIN
pg_attribute a ON a.attrelid = t.oid AND a.attnum = k.attnum
pg_attribute a ON a.attrelid = t.oid
WHERE
n.nspname = $1
AND t.relname = $2
Expand Down Expand Up @@ -389,17 +328,14 @@ async def get_constraint_details(conn_id: str, schema: str, table: str, constrai
WHEN c.contype = 'x' THEN 'EXCLUSION'
ELSE 'OTHER'
END as constraint_type_desc,
obj_description(c.oid) as description,
pg_get_constraintdef(c.oid) as definition,
CASE
WHEN c.contype = 'f' THEN
(SELECT nspname FROM pg_namespace WHERE oid = ref_table.relnamespace) || '.' || ref_table.relname
ELSE NULL
END as referenced_table,
ARRAY_AGG(col.attname ORDER BY u.attposition) as column_names,
CASE
WHEN c.contype = 'f' THEN
ARRAY_AGG(ref_col.attname ORDER BY u2.attposition)
ARRAY_AGG(ref_col.attname)
ELSE NULL
END as referenced_columns
FROM
Expand All @@ -411,13 +347,9 @@ async def get_constraint_details(conn_id: str, schema: str, table: str, constrai
LEFT JOIN
pg_class ref_table ON ref_table.oid = c.confrelid
LEFT JOIN
LATERAL unnest(c.conkey) WITH ORDINALITY AS u(attnum, attposition) ON TRUE
LEFT JOIN
pg_attribute col ON col.attrelid = t.oid AND col.attnum = u.attnum
LEFT JOIN
LATERAL unnest(c.confkey) WITH ORDINALITY AS u2(attnum, attposition) ON c.contype = 'f'
pg_attribute col ON col.attrelid = t.oid
LEFT JOIN
pg_attribute ref_col ON c.contype = 'f' AND ref_col.attrelid = c.confrelid AND ref_col.attnum = u2.attnum
pg_attribute ref_col ON c.contype = 'f' AND ref_col.attrelid = c.confrelid
WHERE
n.nspname = $1
AND t.relname = $2
Expand Down
2 changes: 1 addition & 1 deletion server/tools/query.py
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Expand Up @@ -78,7 +78,7 @@ async def pg_explain(query: str, conn_id: str, params=None):
Complete JSON-formatted execution plan
"""
# Prepend EXPLAIN to the query
explain_query = f"EXPLAIN (FORMAT JSON) {query}"
explain_query = f"EXPLAIN {query}"

# Execute the explain query
result = await execute_query(explain_query, conn_id, params)
Expand Down
4 changes: 2 additions & 2 deletions test.py
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Expand Up @@ -233,7 +233,7 @@ async def run(connection_string: str | None):
print(f"Error fetching extensions: {e}")

# Find a schema with tables to test table resources
for schema_idx, schema in enumerate(schemas_data[:3]):
for schema_idx, schema in enumerate(schemas_data[:10]):
schema_name = schema.get('schema_name')

print(f"\nTesting tables for schema '{schema_name}'...")
Expand Down Expand Up @@ -292,7 +292,7 @@ async def run(connection_string: str | None):
break

# Test disconnect tool if available
break # Exit schema loop once we've found a table
# break # Exit schema loop once we've found a table
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@kneth kneth Apr 3, 2025

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Can the break be removed?

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@amotl amotl Apr 3, 2025

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It can be removed, sure. I didn't want to change too much compared to the original, that's why it's just a comment.

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@amotl amotl Apr 3, 2025

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Please also note this PR is just for visibility purposes. It will probably never be merged, at least not in its current form.

except json.JSONDecodeError:
print(f"Error parsing schemas: {content_item.text[:100]}")

Expand Down