Add PostgreSQL support to MCP Database Server

Updated package.json and package-lock.json to include PostgreSQL dependencies. Enhanced README with PostgreSQL usage instructions and configuration details. Modified index.ts to handle PostgreSQL connection parameters and logging. Added PostgresqlAdapter for database interactions.

src/db/postgresql-adapter.ts

@@ -0,0 +1,185 @@
+import { DbAdapter } from "./adapter.js";
+import pg from 'pg';
+
+/**
+ * PostgreSQL database adapter implementation
+ */
+export class PostgresqlAdapter implements DbAdapter {
+  private client: pg.Client | null = null;
+  private config: pg.ClientConfig;
+  private host: string;
+  private database: string;
+
+  constructor(connectionInfo: {
+    host: string;
+    database: string;
+    user?: string;
+    password?: string;
+    port?: number;
+    ssl?: boolean | object;
+    options?: any;
+  }) {
+    this.host = connectionInfo.host;
+    this.database = connectionInfo.database;
+    
+    // Create PostgreSQL connection config
+    this.config = {
+      host: connectionInfo.host,
+      database: connectionInfo.database,
+      port: connectionInfo.port || 5432,
+      user: connectionInfo.user,
+      password: connectionInfo.password,
+      ssl: connectionInfo.ssl
+    };
+  }
+
+  /**
+   * Initialize PostgreSQL connection
+   */
+  async init(): Promise<void> {
+    try {
+      console.error(`[INFO] Connecting to PostgreSQL: ${this.host}, Database: ${this.database}`);
+      this.client = new pg.Client(this.config);
+      await this.client.connect();
+      console.error(`[INFO] PostgreSQL connection established successfully`);
+    } catch (err) {
+      console.error(`[ERROR] PostgreSQL connection error: ${(err as Error).message}`);
+      throw new Error(`Failed to connect to PostgreSQL: ${(err as Error).message}`);
+    }
+  }
+
+  /**
+   * Execute a SQL query and get all results
+   * @param query SQL query to execute
+   * @param params Query parameters
+   * @returns Promise with query results
+   */
+  async all(query: string, params: any[] = []): Promise<any[]> {
+    if (!this.client) {
+      throw new Error("Database not initialized");
+    }
+
+    try {
+      // PostgreSQL uses $1, $2, etc. for parameterized queries
+      const preparedQuery = query.replace(/\?/g, (_, i) => `$${i + 1}`);
+      
+      const result = await this.client.query(preparedQuery, params);
+      return result.rows;
+    } catch (err) {
+      throw new Error(`PostgreSQL query error: ${(err as Error).message}`);
+    }
+  }
+
+  /**
+   * Execute a SQL query that modifies data
+   * @param query SQL query to execute
+   * @param params Query parameters
+   * @returns Promise with result info
+   */
+  async run(query: string, params: any[] = []): Promise<{ changes: number, lastID: number }> {
+    if (!this.client) {
+      throw new Error("Database not initialized");
+    }
+
+    try {
+      // Replace ? with numbered parameters
+      const preparedQuery = query.replace(/\?/g, (_, i) => `$${i + 1}`);
+      
+      let lastID = 0;
+      let changes = 0;
+      
+      // For INSERT queries, try to get the inserted ID
+      if (query.trim().toUpperCase().startsWith('INSERT')) {
+        // Add RETURNING clause to get the inserted ID if it doesn't already have one
+        const returningQuery = preparedQuery.includes('RETURNING') 
+          ? preparedQuery 
+          : `${preparedQuery} RETURNING id`;
+          
+        const result = await this.client.query(returningQuery, params);
+        changes = result.rowCount || 0;
+        lastID = result.rows[0]?.id || 0;
+      } else {
+        const result = await this.client.query(preparedQuery, params);
+        changes = result.rowCount || 0;
+      }
+      
+      return { changes, lastID };
+    } catch (err) {
+      throw new Error(`PostgreSQL query error: ${(err as Error).message}`);
+    }
+  }
+
+  /**
+   * Execute multiple SQL statements
+   * @param query SQL statements to execute
+   * @returns Promise that resolves when execution completes
+   */
+  async exec(query: string): Promise<void> {
+    if (!this.client) {
+      throw new Error("Database not initialized");
+    }
+
+    try {
+      await this.client.query(query);
+    } catch (err) {
+      throw new Error(`PostgreSQL batch error: ${(err as Error).message}`);
+    }
+  }
+
+  /**
+   * Close the database connection
+   */
+  async close(): Promise<void> {
+    if (this.client) {
+      await this.client.end();
+      this.client = null;
+    }
+  }
+
+  /**
+   * Get database metadata
+   */
+  getMetadata(): { name: string, type: string, server: string, database: string } {
+    return {
+      name: "PostgreSQL",
+      type: "postgresql",
+      server: this.host,
+      database: this.database
+    };
+  }
+
+  /**
+   * Get database-specific query for listing tables
+   */
+  getListTablesQuery(): string {
+    return "SELECT table_name as name FROM information_schema.tables WHERE table_schema = 'public' ORDER BY table_name";
+  }
+
+  /**
+   * Get database-specific query for describing a table
+   * @param tableName Table name
+   */
+  getDescribeTableQuery(tableName: string): string {
+    return `
+      SELECT 
+        c.column_name as name,
+        c.data_type as type,
+        CASE WHEN c.is_nullable = 'NO' THEN 1 ELSE 0 END as notnull,
+        CASE WHEN pk.constraint_name IS NOT NULL THEN 1 ELSE 0 END as pk,
+        c.column_default as dflt_value
+      FROM 
+        information_schema.columns c
+      LEFT JOIN 
+        information_schema.key_column_usage kcu 
+        ON c.table_name = kcu.table_name AND c.column_name = kcu.column_name
+      LEFT JOIN 
+        information_schema.table_constraints pk 
+        ON kcu.constraint_name = pk.constraint_name AND pk.constraint_type = 'PRIMARY KEY'
+      WHERE 
+        c.table_name = '${tableName}'
+        AND c.table_schema = 'public'
+      ORDER BY 
+        c.ordinal_position
+    `;
+  }
+}