add distinctOn for postgres

Author: artzhookov

lib/dialects/postgresql/blocks.js

@@ -41,4 +41,23 @@ module.exports = function(dialect) {
 	dialect.blocks.add('explain:verbose', function() {
 		return 'verbose';
 	});
-};
+
+	dialect.blocks.add('distinctOn', function(params) {
+		var distinctOn = params.distinctOn;
+		var result = '';
+
+		if (_.isString(distinctOn)) distinctOn = [distinctOn];
+
+		if (_.isArray(distinctOn)) {
+			result = _(distinctOn).map(function(distinctOnField) {
+				return dialect._wrapIdentifier(distinctOnField);
+			}).join(', ');
+		}
+
+		if (result) {
+			result = 'distinct on (' + result + ')';
+		}
+
+		return result;
+	});
+};

lib/dialects/postgresql/templates.js

@@ -33,4 +33,17 @@ module.exports = function(dialect) {
 			templateChecks.propType(type, params, 'verbose', 'boolean');
 		}
 	});
+
+	// patch parent select to add some blocks
+	var selectTemplate = dialect.templates.get('select');
+	selectTemplate.pattern = selectTemplate.pattern.replace('{distinct}', '{distinct} {distinctOn}');
+
+	var parentSelectValidate = selectTemplate.validate;
+	selectTemplate.validate = function(type, params) {
+		parentSelectValidate(type, params);
+
+		templateChecks.propType(type, params, 'distinctOn', ['string', 'array']);
+	};
+
+	dialect.templates.set('select', selectTemplate);
 };

tests/6_dialects/0_postgresql.js

@@ -261,4 +261,26 @@ describe('PostgreSQL dialect', function() {
 		});
 
 	});
+
+	describe('select', function() {
+		describe('distinctOn', function() {
+			it('should be ok with string value', function() {
+				var result = jsonSql.build({
+					table: 'users',
+					distinctOn: 'a'
+				});
+
+				expect(result.query).to.be.equal('select distinct on ("a") * from "users";');
+			});
+
+			it('should be ok with array value', function() {
+				var result = jsonSql.build({
+					table: 'users',
+					distinctOn: ['a', 'b']
+				});
+
+				expect(result.query).to.be.equal('select distinct on ("a", "b") * from "users";');
+			});
+		});
+	});
 });