feat(mssql): table hints (#8843)

docs/querying.md

@@ -431,3 +431,19 @@ Subtask.findAll({
   order: sequelize.col('age')
 })
 ```
+
+## Table Hint
+
+`tableHint` can be used to optionally pass a table hint when using mssql. The hint must be a value from `Sequelize.TableHints` and should only be used when absolutely necessary. Only a single table hint is currently supported per query. 
+
+Table hints override the default behavior of mssql query optimizer by specifing certain options. They only affect the table or view referenced in that clause.
+
+```js
+const TableHints = Sequelize.TableHints;
+
+Project.findAll({
+  // adding the table hint NOLOCK
+  tableHint: TableHints.NOLOCK
+  // this will generate the SQL 'WITH (NOLOCK)'
+})
+```

lib/dialects/mssql/query-generator.js

@@ -3,6 +3,7 @@
 const _ = require('lodash');
 const Utils = require('../../utils');
 const DataTypes = require('../../data-types');
+const TableHints = require('../../table-hints');
 const AbstractQueryGenerator = require('../abstract/query-generator');
 const randomBytes = require('crypto').randomBytes;
 const semver = require('semver');
@@ -815,6 +816,10 @@ const QueryGenerator = {
       mainFragment += ' AS ' + mainTableAs;
     }
 
+    if (options.tableHint && TableHints[options.tableHint]) {
+      mainFragment += ` WITH (${TableHints[options.tableHint]})`;
+    }
+
     return mainFragment;
   },
 

lib/sequelize.js

@@ -12,6 +12,7 @@ const ModelManager = require('./model-manager');
 const QueryInterface = require('./query-interface');
 const Transaction = require('./transaction');
 const QueryTypes = require('./query-types');
+const TableHints = require('./table-hints');
 const sequelizeErrors = require('./errors');
 const Promise = require('./promise');
 const Hooks = require('./hooks');
@@ -1164,6 +1165,11 @@ Sequelize.prototype.Promise = Sequelize.Promise = Promise;
  */
 Sequelize.prototype.QueryTypes = Sequelize.QueryTypes = QueryTypes;
 
+/**
+ * Available table hints to be used for querying data in mssql for table hints
+ * @see {@link TableHints}
+ */
+Sequelize.prototype.TableHints = Sequelize.TableHints = TableHints;
 
 /**
  * Operators symbols to be used for querying data

lib/table-hints.js

+'use strict';
+
+/**
+ * An enum of table hints to be used in mssql for querying with table hints
+ * 
+ * @property NOLOCK
+ * @property READUNCOMMITTED
+ * @property UPDLOCK
+ * @property REPEATABLEREAD
+ * @property SERIALIZABLE
+ * @property READCOMMITTED
+ * @property TABLOCK
+ * @property TABLOCKX
+ * @property PAGLOCK
+ * @property ROWLOCK
+ * @property NOWAIT
+ * @property READPAST
+ * @property XLOCK
+ * @property SNAPSHOT
+ * @property NOEXPAND
+ */
+const TableHints = module.exports = { // eslint-disable-line
+  NOLOCK: 'NOLOCK',
+  READUNCOMMITTED: 'READUNCOMMITTED',
+  UPDLOCK: 'UPDLOCK',
+  REPEATABLEREAD: 'REPEATABLEREAD',
+  SERIALIZABLE: 'SERIALIZABLE',
+  READCOMMITTED: 'READCOMMITTED',
+  TABLOCK: 'TABLOCK',
+  TABLOCKX: 'TABLOCKX',
+  PAGLOCK: 'PAGLOCK',
+  ROWLOCK: 'ROWLOCK',
+  NOWAIT: 'NOWAIT',
+  READPAST: 'READPAST',
+  XLOCK: 'XLOCK',
+  SNAPSHOT: 'SNAPSHOT',
+  NOEXPAND: 'NOEXPAND'
+};

test/unit/dialects/mssql/query-generator.test.js

@@ -4,6 +4,7 @@ const Support = require(__dirname + '/../../support');
 const expectsql = Support.expectsql;
 const current = Support.sequelize;
 const Operators = require('../../../../lib/operators');
+const TableHints = require('../../../../lib/table-hints');
 const QueryGenerator = require('../../../../lib/dialects/mssql/query-generator');
 const _ = require('lodash');
 
@@ -63,6 +64,16 @@ if (current.dialect.name === 'mssql') {
         mssql: 'SELECT id, name FROM myTable AS myOtherName'
       });
 
+      // With tableHint - nolock
+      expectsql(modifiedGen.selectFromTableFragment({ tableHint: TableHints.NOLOCK }, { primaryKeyField: 'id' }, ['id', 'name'], 'myTable', 'myOtherName'), {
+        mssql: 'SELECT id, name FROM myTable AS myOtherName WITH (NOLOCK)'
+      });
+
+      // With tableHint - NOWAIT
+      expectsql(modifiedGen.selectFromTableFragment({ tableHint: TableHints.NOWAIT }, { primaryKeyField: 'id' }, ['id', 'name'], 'myTable', 'myOtherName'), {
+        mssql: 'SELECT id, name FROM myTable AS myOtherName WITH (NOWAIT)'
+      });
+
       // With limit
       expectsql(modifiedGen.selectFromTableFragment({ limit: 10 }, { primaryKeyField: 'id' }, ['id', 'name'], 'myTable', 'myOtherName'), {
         mssql: 'SELECT id, name FROM myTable AS myOtherName'