feat: support ifNotExists when creating a postgres db

Signed-off-by: Andy Burke <andy.burke@mailbox.earth>

Author: andyburke

index.js

@@ -88,12 +88,38 @@ var PgDriver = Base.extend({
   createDatabase: function (dbName, options, callback) {
     var spec = '';
 
-    if (typeof options === 'function') callback = options;
+    if (typeof options === 'function') {
+      callback = options;
+      options = {};
+    }
 
-    this.runSql(
-      util.format('CREATE DATABASE %s %s', this.escapeDDL(dbName), spec),
-      callback
-    );
+    if (options.ifNotExists) {
+      this.runSql(
+        `
+        DO
+        $do$
+        DECLARE
+          _db TEXT := '${ dbName }';
+        BEGIN
+          CREATE EXTENSION IF NOT EXISTS dblink;
+          IF EXISTS (SELECT 1 FROM pg_database WHERE datname = _db) THEN
+            RAISE NOTICE 'Database "%" already exists, skipping creation.', _db;
+          ELSE
+            PERFORM dblink_connect('dbname=' || current_database());
+            PERFORM dblink_exec('CREATE DATABASE ' || _db || ' ${ spec }');
+          END IF;
+        END
+        $do$
+        `,
+        callback
+      );
+    }
+    else {
+      this.runSql(
+        util.format('CREATE DATABASE %s %s', this.escapeDDL(dbName), spec),
+        callback
+      );
+    }
   },
 
   dropDatabase: function (dbName, options, callback) {

package-lock.json

@@ -30,14 +30,14 @@
   },
   "homepage": "https://github.com/db-migrate/pg",
   "dependencies": {
-    "bluebird": "^3.1.1",
+    "bluebird": "^3.7.2",
     "db-migrate-base": "^2.0.0",
-    "pg": "^7.8.0",
-    "semver": "^5.0.3"
+    "pg": "^7.14.0",
+    "semver": "^6.3.0"
   },
   "devDependencies": {
-    "db-meta": "^0.4.1",
-    "db-migrate-shared": "^1.1.2",
-    "vows": "0.8.0"
+    "db-meta": "^0.5.1",
+    "db-migrate-shared": "^1.2.0",
+    "vows": "0.8.3"
   }
 }

package.json

@@ -57,6 +57,37 @@ vows
       }
     }
   })
+  .addBatch({
+    createDatabase: {
+      topic: function () {
+        db.createDatabase(
+          'test',
+          this.callback.bind(this)
+        );
+      },
+
+      'created database': function (err) {
+        assert.isNotNull(err);
+      }
+    }
+  })
+  .addBatch({
+    'create existing database': {
+      topic: function () {
+        db.createDatabase(
+          'test',
+          {
+            ifNotExists: true
+          },
+          this.callback.bind(this)
+        );
+      },
+
+      'created existing database': function (err) {
+        assert.isNotNull(err);
+      }
+    }
+  })
   .addBatch({
     createTable: {
       topic: function () {