AlaSQL#2027 sqlCache retains data (and other properties), possible me…

…mory leak AlaSQL#2027

- Remove the `data` property from the sql cache after executing the query

src/17alasql.js

@@ -244,6 +244,23 @@ alasql.exec = function (sql, params, cb, scope) {
 	}
 };
 
+/**
+ * Clears any unneeded properties from a given AST statement closure used for caching
+ * @param {Object} statement the statement to cleanup
+ */
+function cleanupCache(statement) {
+	if (!statement) {
+		return;
+	}
+	if (!alasql.options.cache) {
+		return;
+	}
+	// cleanup the table data to prevent storing this information in the SQL cache
+	if (statement && statement.query && statement.query.data) {
+		statement.query.data = [];
+	}
+}
+
 /**
  Run SQL statement on specific database
  */
@@ -259,7 +276,9 @@ alasql.dexec = function (databaseid, sql, params, cb, scope) {
 		let statement = db.sqlCache[hh];
 		// If database structure was not changed since last time return cache
 		if (statement && db.dbversion === statement.dbversion) {
-			return statement(params, cb);
+			var res = statement(params, cb);
+			cleanupCache(statement);
+			return res;
 		}
 	}
 
@@ -302,6 +321,7 @@ alasql.dexec = function (databaseid, sql, params, cb, scope) {
 				db.sqlCache[hh] = statement;
 			}
 			var res = (alasql.res = statement(params, cb, scope));
+			cleanupCache(statement);
 			return res;
 		}
 		alasql.precompile(ast.statements[0], alasql.useid, params);

test/test2027.js

@@ -0,0 +1,30 @@
+const alasql = require('../dist/alasql.js');
+
+if (typeof exports === 'object') {
+	var assert = require('assert');
+}
+
+describe('Test 2007 - SQL cache', function () {
+	before(function () {
+		alasql('create database test');
+		alasql('use test');
+	});
+
+	after(function () {
+		alasql('drop database test');
+	});
+
+	it('A) Execute query and assert cache for `data` afterwards', () => {
+		alasql('CREATE TABLE osoby (id INT, meno STRING)');
+		alasql('INSERT INTO osoby VALUES (1, "John"), (2, "Jane"), (3, "Jake")');
+		alasql('SELECT * FROM osoby');
+
+		assert.deepEqual(alasql.databases["test"].sqlCache["-169125189"].query.data, []);
+
+		// Execute same query from cache again, the cache is hit now
+		alasql('SELECT * FROM osoby');
+
+		// Cache should still be empty for "data"
+		assert.deepEqual(alasql.databases["test"].sqlCache["-169125189"].query.data, []);
+	});
+});