database_mcp_sqlite/tools/
read_query.rs

1//! MCP tool: `read_query`.
2
3use std::borrow::Cow;
4
5use database_mcp_server::AppError;
6use database_mcp_server::types::QueryResponse;
7use database_mcp_sql::Connection as _;
8use database_mcp_sql::validation::validate_read_only_with_dialect;
9use rmcp::handler::server::router::tool::{AsyncTool, ToolBase};
10use rmcp::model::{ErrorData, ToolAnnotations};
11use serde_json::Value;
12
13use crate::SqliteHandler;
14use crate::types::QueryRequest;
15
16/// Marker type for the `read_query` MCP tool.
17pub(crate) struct ReadQueryTool;
18
19impl ReadQueryTool {
20    const NAME: &'static str = "read_query";
21    const DESCRIPTION: &'static str = r#"Execute a read-only SQL query. Allowed statements: SELECT.
22
23<usecase>
24Use when:
25- Querying data from tables (SELECT with WHERE, JOIN, GROUP BY, etc.)
26- Aggregations: COUNT, SUM, AVG, GROUP BY, HAVING
27- Checking data existence or counts
28</usecase>
29
30<when_not_to_use>
31- Data changes (INSERT, UPDATE, DELETE) → use write_query
32- Query performance analysis → use explain_query
33- Discovering tables or columns → use list_tables or get_table_schema
34</when_not_to_use>
35
36<examples>
37✓ "SELECT * FROM users WHERE status = 'active'"
38✓ "SELECT COUNT(*) FROM orders GROUP BY region"
39✗ "INSERT INTO users ..." → use write_query
40✗ "EXPLAIN SELECT ..." → use explain_query for structured analysis
41</examples>
42
43<what_it_returns>
44A JSON array of row objects, each keyed by column name.
45</what_it_returns>"#;
46}
47
48impl ToolBase for ReadQueryTool {
49    type Parameter = QueryRequest;
50    type Output = QueryResponse;
51    type Error = ErrorData;
52
53    fn name() -> Cow<'static, str> {
54        Self::NAME.into()
55    }
56
57    fn description() -> Option<Cow<'static, str>> {
58        Some(Self::DESCRIPTION.into())
59    }
60
61    fn annotations() -> Option<ToolAnnotations> {
62        Some(
63            ToolAnnotations::new()
64                .read_only(true)
65                .destructive(false)
66                .idempotent(true)
67                .open_world(true),
68        )
69    }
70}
71
72impl AsyncTool<SqliteHandler> for ReadQueryTool {
73    async fn invoke(handler: &SqliteHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
74        Ok(handler.read_query(&params).await?)
75    }
76}
77
78impl SqliteHandler {
79    /// Executes a read-only SQL query.
80    ///
81    /// Validates that the query is read-only before executing.
82    ///
83    /// # Errors
84    ///
85    /// Returns [`AppError::ReadOnlyViolation`] if the query is not
86    /// read-only, or [`AppError::Query`] if the backend reports an error.
87    pub async fn read_query(&self, request: &QueryRequest) -> Result<QueryResponse, AppError> {
88        validate_read_only_with_dialect(&request.query, &sqlparser::dialect::SQLiteDialect {})?;
89        let rows = self.connection.fetch(request.query.as_str(), None).await?;
90        Ok(QueryResponse {
91            rows: Value::Array(rows),
92        })
93    }
94}
95
96#[cfg(test)]
97mod tests {
98    use serde_json::Value;
99    use sqlx::SqlitePool;
100    use sqlx::sqlite::SqlitePoolOptions;
101    use sqlx::sqlite::SqliteRow;
102    use sqlx_to_json::RowExt;
103
104    async fn mem_pool() -> SqlitePool {
105        SqlitePoolOptions::new()
106            .max_connections(1)
107            .connect("sqlite::memory:")
108            .await
109            .expect("in-memory SQLite")
110    }
111
112    async fn query_json(pool: &SqlitePool, sql: &str) -> Value {
113        let rows: Vec<SqliteRow> = sqlx::query(sql).fetch_all(pool).await.expect("query failed");
114        Value::Array(rows.iter().map(RowExt::to_json).collect())
115    }
116
117    #[tokio::test]
118    async fn rows_to_json_array_empty_result() {
119        let pool = mem_pool().await;
120        sqlx::query("CREATE TABLE t (v INTEGER)").execute(&pool).await.unwrap();
121
122        let rows = query_json(&pool, "SELECT v FROM t").await;
123        assert_eq!(rows, Value::Array(vec![]));
124    }
125
126    #[tokio::test]
127    async fn rows_to_json_array_multiple_rows() {
128        let pool = mem_pool().await;
129        sqlx::query("CREATE TABLE t (id INTEGER, name TEXT, score REAL)")
130            .execute(&pool)
131            .await
132            .unwrap();
133        sqlx::query("INSERT INTO t VALUES (1, 'alice', 9.5), (2, 'bob', 8.0)")
134            .execute(&pool)
135            .await
136            .unwrap();
137
138        let rows = query_json(&pool, "SELECT id, name, score FROM t ORDER BY id").await;
139        assert_eq!(rows.as_array().expect("should be array").len(), 2);
140
141        assert_eq!(rows[0]["id"], Value::Number(1.into()));
142        assert_eq!(rows[0]["name"], Value::String("alice".into()));
143        assert!(rows[0]["score"].is_number());
144
145        assert_eq!(rows[1]["id"], Value::Number(2.into()));
146        assert_eq!(rows[1]["name"], Value::String("bob".into()));
147    }
148}
database_mcp_sqlite/tools/read_query.rs

database_mcp_sqlite/tools/
read_query.rs
