Fix Postgres showIndex not returning functional indices

changelog.md

 # Next
+- [FIXED] Show indexes query on Postgres fails to return functional indexes [#3911](https://github.com/sequelize/sequelize/issues/3911)
 - [FIXED] Custom field names in json queries
 - [FIXED] JSON cast key using the equality operator. [#3824](https://github.com/sequelize/sequelize/issues/3824)
 - [FIXED] Map column names with `.field` in scopes with includes. [#4210](https://github.com/sequelize/sequelize/issues/4210)

lib/dialects/postgres/query-generator.js

@@ -439,7 +439,7 @@ var QueryGenerator = {
     var query = 'SELECT i.relname AS name, ix.indisprimary AS primary, ix.indisunique AS unique, ix.indkey AS indkey, ' +
       'array_agg(a.attnum) as column_indexes, array_agg(a.attname) AS column_names, pg_get_indexdef(ix.indexrelid) ' +
       'AS definition FROM pg_class t, pg_class i, pg_index ix, pg_attribute a ' +
-      'WHERE t.oid = ix.indrelid AND i.oid = ix.indexrelid AND a.attrelid = t.oid AND a.attnum = ANY(ix.indkey) AND '+
+      'WHERE t.oid = ix.indrelid AND i.oid = ix.indexrelid AND a.attrelid = t.oid AND '+
       "t.relkind = 'r' and t.relname = '<%= tableName %>' GROUP BY i.relname, ix.indexrelid, ix.indisprimary, ix.indisunique, ix.indkey ORDER BY i.relname;";
 
     return Utils._.template(query)({ tableName: tableName });

lib/dialects/postgres/query.js

@@ -170,6 +170,10 @@ Query.prototype.run = function(sql) {
         // Indkey is the order of attributes in the index, specified by a string of attribute indexes
         result.fields = result.indkey.split(' ').map(function (indKey, index) {
           field = columns[indKey];
+          // for functional indices indKey = 0
+          if(!field) {
+            return null;
+          }
           attribute = attributes[index];
           return {
             attribute: field,
@@ -177,7 +181,7 @@ Query.prototype.run = function(sql) {
             order: attribute.indexOf('DESC') !== -1 ? 'DESC' : attribute.indexOf('ASC') !== -1 ? 'ASC': undefined,
             length: undefined
           };
-        });
+        }).filter(function(n){ return n !== null; });
         delete result.columns;
       });
       return results;

test/integration/dialects/postgres/query-interface.test.js

+'use strict';
+
+/* jshint -W030 */
+var chai = require('chai')
+  , expect = chai.expect
+  , Support = require(__dirname + '/../../support')
+  , dialect = Support.getTestDialect()
+  , DataTypes = require(__dirname + '/../../../../lib/data-types')
+  , _ = require('lodash');
+
+if (dialect.match(/^postgres/)) {
+  describe('[POSTGRES Specific] QueryInterface', function () {
+    beforeEach(function () {
+      this.sequelize.options.quoteIdenifiers = true;
+      this.queryInterface = this.sequelize.getQueryInterface();
+    });
+
+    describe('indexes', function () {
+      beforeEach(function () {
+        var self = this;
+        return this.queryInterface.dropTable('Group').then(function () {
+          return self.queryInterface.createTable('Group', {
+            username: DataTypes.STRING,
+            isAdmin: DataTypes.BOOLEAN,
+            from: DataTypes.STRING
+          });
+        });
+      });
+
+      it('adds, reads and removes a named functional index to the table', function () {
+        var self = this;
+        return this.queryInterface.addIndex('Group', [this.sequelize.fn('lower', this.sequelize.col('username'))], {
+          name: 'group_username_lower'
+        }).then(function () {
+          return self.queryInterface.showIndex('Group').then(function (indexes) {
+            var indexColumns = _.uniq(indexes.map(function (index) {
+              return index.name;
+            }));
+            expect(indexColumns).to.include('group_username_lower');
+            return self.queryInterface.removeIndex('Group', 'group_username_lower').then(function () {
+              return self.queryInterface.showIndex('Group').then(function (indexes) {
+                indexColumns = _.uniq(indexes.map(function (index) {
+                  return index.name;
+                }));
+                expect(indexColumns).to.be.empty;
+              });
+            });
+          });
+        });
+      });
+    });
+  });
+}