feat: query to fetch unique columns

Signed-off-by: Muhammad Aaqil <aaqilcs102@gmail.com>

lib/datasource.js

@@ -1308,6 +1308,40 @@ DataSource.prototype.discoverPrimaryKeys = function(modelName, options, cb) {
   return cb.promise;
 };
 
+/**
+ * Discover unique keys for a given modelName.
+ * Callback function return value is an object that can have the following properties:
+ *
+ *| Key | Type | Description |
+ *|-----|------|-------------|
+ *| owner |String | Table schema or owner (may be null). Owner defaults to current user.
+ *| tableName |String| Table name
+ *| columnName |String| Column name
+ * See [ID Properties](./Model-definition-JSON-file.html#id-properties) for more
+ * information.
+ * @param {String} modelName The model name
+ * @options {Object} options The options
+ * @param {Function} [cb] The callback function
+ * @returns {Promise} A promise with an array of Primary Keys (Property[])
+ */
+DataSource.prototype.discoverUniqueKeys = function(modelName, options, cb) {
+  this.freeze();
+
+  if (cb === undefined && typeof options === 'function') {
+    cb = options;
+    options = {};
+  }
+  options = options || {};
+  cb = cb || utils.createPromiseCallback();
+
+  if (this.connector.discoverUniqueKeys) {
+    this.connector.discoverUniqueKeys(modelName, options, cb);
+  } else if (cb) {
+    process.nextTick(cb);
+  }
+  return cb.promise;
+};
+
 /*! Method will be completely removed in LoopBack.next
 */
 /**
@@ -1619,7 +1653,8 @@ DataSource.prototype.discoverSchemas = function(tableName, options, cb) {
 
   const tasks = [
     this.discoverModelProperties.bind(this, tableName, options),
-    this.discoverPrimaryKeys.bind(this, tableName, options)];
+    this.discoverPrimaryKeys.bind(this, tableName, options),
+    this.discoverUniqueKeys.bind(this, tableName, options)];
 
   const followingRelations = options.associations || options.relations;
   if (followingRelations) {
@@ -1633,6 +1668,14 @@ DataSource.prototype.discoverSchemas = function(tableName, options, cb) {
     }
 
     const columns = results[0];
+    const uniqueKeyArray = results[2] || [];
+
+    let uniqueKeys = [];
+
+    uniqueKeyArray.forEach(key => {
+      uniqueKeys.push(key['columnName']);
+    });
+
     if (!columns || columns.length === 0) {
       cb(new Error(g.f('Table \'%s\' does not exist.', tableName)));
       return cb.promise;
@@ -1649,6 +1692,7 @@ DataSource.prototype.discoverSchemas = function(tableName, options, cb) {
       debug('Primary keys: ', pks);
     }
 
+    uniqueKeys = uniqueKeys.filter(item => !pks.hasOwnProperty(item));
     const schema = {
       name: nameMapper('table', tableName),
       options: {
@@ -1677,6 +1721,9 @@ DataSource.prototype.discoverSchemas = function(tableName, options, cb) {
       if (pks[item.columnName]) {
         schema.properties[propName].id = pks[item.columnName];
       }
+      if (uniqueKeys.includes(propName)) {
+        schema.properties[propName]['index'] = {unique: true};
+      }
       const dbSpecific = schema.properties[propName][dbType] = {
         columnName: item.columnName,
         dataType: item.dataType,