fix(sync): handle alter correctly with underscored/aliased columns (#10872)

lib/model.js

@@ -1296,7 +1296,7 @@ class Model {
             const removedConstraints = {};
 
             _.each(attributes, (columnDesc, columnName) => {
-              if (!columns[columnName]) {
+              if (!columns[columnName] && !columns[attributes[columnName].field]) {
                 changes.push(() => this.QueryInterface.addColumn(this.getTableName(options), attributes[columnName].field || columnName, attributes[columnName]));
               }
             });

test/integration/sequelize.test.js

@@ -1120,6 +1120,20 @@ describe(Support.getTestDialectTeaser('Sequelize'), () => {
       });
     });
 
+    it('handles alter: true with underscore correctly', function() {
+      this.sequelize.define('access_metric', {
+        user_id: {
+          type: DataTypes.INTEGER
+        }
+      }, {
+        underscored: true
+      });
+
+      return this.sequelize.sync({
+        alter: true
+      });
+    });
+
     describe("doesn't emit logging when explicitly saying not to", () => {
       afterEach(function() {
         this.sequelize.options.logging = false;