database_mcp_postgres/tools/
write_query.rs

1//! MCP tool: `write_query`.
2
3use std::borrow::Cow;
4
5use database_mcp_server::AppError;
6use database_mcp_server::types::{QueryRequest, QueryResponse};
7use database_mcp_sql::Connection as _;
8use rmcp::handler::server::router::tool::{AsyncTool, ToolBase};
9use rmcp::model::{ErrorData, ToolAnnotations};
10use serde_json::Value;
11
12use crate::PostgresHandler;
13
14/// Marker type for the `write_query` MCP tool.
15pub(crate) struct WriteQueryTool;
16
17impl WriteQueryTool {
18    const NAME: &'static str = "write_query";
19    const DESCRIPTION: &'static str = r#"Execute a write SQL query (INSERT, UPDATE, DELETE, CREATE, ALTER, DROP).
20
21<usecase>
22Use when:
23- Inserting, updating, or deleting rows
24- Creating or altering tables, indexes, views, or other schema objects
25- Any data modification operation
26</usecase>
27
28<when_not_to_use>
29- Read-only queries (SELECT, SHOW) → use read_query
30- Query performance analysis → use explain_query
31- Creating/dropping entire databases → use create_database or drop_database
32</when_not_to_use>
33
34<examples>
35✓ "INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com')"
36✓ "UPDATE orders SET status = 'shipped' WHERE id = 42"
37✓ "CREATE TABLE logs (id SERIAL PRIMARY KEY, message TEXT)"
38✗ "SELECT * FROM users" → use read_query
39</examples>
40
41<what_it_returns>
42A JSON array of affected/returning row objects, each keyed by column name.
43</what_it_returns>"#;
44}
45
46impl ToolBase for WriteQueryTool {
47    type Parameter = QueryRequest;
48    type Output = QueryResponse;
49    type Error = ErrorData;
50
51    fn name() -> Cow<'static, str> {
52        Self::NAME.into()
53    }
54
55    fn description() -> Option<Cow<'static, str>> {
56        Some(Self::DESCRIPTION.into())
57    }
58
59    fn annotations() -> Option<ToolAnnotations> {
60        Some(
61            ToolAnnotations::new()
62                .read_only(false)
63                .destructive(true)
64                .idempotent(false)
65                .open_world(true),
66        )
67    }
68}
69
70impl AsyncTool<PostgresHandler> for WriteQueryTool {
71    async fn invoke(handler: &PostgresHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
72        Ok(handler.write_query(&params).await?)
73    }
74}
75
76impl PostgresHandler {
77    /// Executes a write SQL query.
78    ///
79    /// # Errors
80    ///
81    /// Returns [`AppError`] if the query fails.
82    pub async fn write_query(&self, request: &QueryRequest) -> Result<QueryResponse, AppError> {
83        let db = Some(request.database_name.trim()).filter(|s| !s.is_empty());
84        let rows = self.connection.fetch(request.query.as_str(), db).await?;
85        Ok(QueryResponse {
86            rows: Value::Array(rows),
87        })
88    }
89}
database_mcp_postgres/tools/write_query.rs

database_mcp_postgres/tools/
write_query.rs
