Alter table queries.

docs/source/guides/migrations.md

@@ -111,6 +111,27 @@ issue</a> or pull request to see this happen sooner.
 </div>
 </div>
 
+#### `#alterTable`
+
+Alter existing tables. Pass the name of the table you want to alter and a callback
+that will receive a table object with which you will be able to create columns
+of different [field types](#field-types) as well as drop existing columns.
+
+```js
+schema.alterTable('articles', function(table) {
+  table.string('title'); // add a title column
+  table.drop('body'); // drop the body column
+});
+```
+
+- `drop` Drops a table column (**not yet supported in SQLite3**)
+
+```js
+schema.alterTable('articles', function(table) {
+  table.drop('title'); // drop the title column
+});
+```
+
 
 #### `#dropTable`
 

lib/grammar/phrasing_schema.js

@@ -110,6 +110,60 @@ module.exports = Mixin.create(/** @lends Phrasing# */ {
     return this._grammar.join(fragments);
   },
 
+  /**
+   * Alter table statement.
+   *
+   * Subclasses should override to customize this query.
+   *
+   * @method
+   * @public
+   * @param {Object} data
+   * @param {String} data.name
+   * @param {Array.<Column>} data.added
+   * @param {Array.<String>} data.dropped
+   * @return {Statement} The statement.
+   */
+  alterTable: function(data) {
+    var quoteField = this._grammar.field.bind(this._grammar);
+    var added = data.added.map(this.addColumn, this);
+    var dropped = data.dropped.map(this.dropColumn, this);
+    var delimited = this._grammar.delimit([].concat(dropped, added));
+    var joined = this._grammar.join(delimited);
+    var fragments = ['ALTER TABLE '];
+    fragments.push(quoteField(data.name), ' ');
+    fragments = fragments.concat(joined);
+    return Statement.create(this._grammar.join(fragments));
+  },
+
+  /**
+   * Add column fragment.
+   *
+   * Subclasses should override to customize this fragment.
+   *
+   * @method
+   * @public
+   * @param {Object} column
+   * @return {Fragment} The fragment.
+   * @see {@link Phrasing#createColumn}
+   */
+  addColumn: function(column) {
+    return this._grammar.join(['ADD COLUMN ', this.createColumn(column)]);
+  },
+
+  /**
+   * Rename column fragment.
+   *
+   * Subclasses should override to customize this fragment.
+   *
+   * @method
+   * @public
+   * @param {String} column
+   * @return {Fragment} The fragment.
+   */
+  dropColumn: function(column) {
+    return this._grammar.join(['DROP COLUMN ', this._grammar.field(column)]);
+  },
+
   /**
    * Drop table statement.
    *

lib/schema/schema.js

@@ -3,6 +3,7 @@
 var _ = require('lodash');
 var BaseQuery = require('../query/base');
 var CreateTableQuery = require('./table/create');
+var AlterTableQuery = require('./table/alter');
 var DropTableQuery = require('./table/drop');
 
 /**
@@ -36,6 +37,24 @@ var Schema = BaseQuery.extend(/** @lends Schema# */ {
    */
   createTable: function() { return this._spawn(CreateTableQuery, arguments); },
 
+  /**
+   * @function Schema~AlterTableCallback
+   * @param {TableAlterer} table The table object on which you can alter a
+   * table, for instance creating and dropping columns.
+   */
+
+  /**
+   * Alter a table.
+   *
+   * @method
+   * @public
+   * @param {String} name The name of the table to alter.
+   * @param {Schema~AlterTableCallback} cb A callback that will allow you to
+   * create and drop table columns.
+   * @return {CreateTableQuery} A query to execute to alter the table.
+   */
+  alterTable: function() { return this._spawn(AlterTableQuery, arguments); },
+
   /**
    * Drop a table.
    *

lib/schema/table/alter.js

@@ -0,0 +1,76 @@
+'use strict';
+
+var _ = require('lodash');
+var BaseQuery = require('../../query/base');
+var ColumnAlterer = require('./column_alterer');
+
+/**
+ * A query that allows altering tables.
+ *
+ * You will not create this query object directly. Instead, you will
+ * receive it via {@link Schema#alterTable}.
+ *
+ * @protected
+ * @constructor AlterTableQuery
+ * @extends BaseQuery
+ */
+var AlterTableQuery = BaseQuery.extend(/** @lends AlterTableQuery# */ {
+  init: function() { throw new Error('AlterTableQuery must be spawned.'); },
+
+  /**
+   * Override of {@link BaseQuery#_create}.
+   *
+   * @method
+   * @private
+   * @see {@link BaseQuery#_create}
+   * @see {@link Schema#alterTable} for parameter details.
+   */
+  _create: function(name, cb) {
+    if (!cb) { throw new Error('Missing callback to create columns.'); }
+    this._super();
+    this._name = name;
+    this._alterer = ColumnAlterer.create();
+
+    cb(this._alterer);
+
+    var pkCount = _(this._alterer.added)
+      .map('options').filter('primaryKey').size();
+    if (pkCount > 1) {
+      throw new Error('Table may only have one primary key column.');
+    }
+  },
+
+  /**
+   * Duplication implementation.
+   *
+   * @method
+   * @protected
+   * @see {@link BaseQuery#_take}
+   */
+  _take: function(orig) {
+    this._super(orig);
+    this._name = orig._name;
+    this._alterer = orig._alterer;
+  },
+
+  /**
+   * Override of {@link BaseQuery#sql}.
+   *
+   * @method
+   * @protected
+   * @see {@link BaseQuery#sql}
+   */
+  sql: function() {
+    return this._adapter.phrasing.alterTable({
+      name: this._name,
+      added: this._alterer.added,
+      dropped: this._alterer.dropped,
+      renamed: this._alterer.renamed
+    });
+  }
+
+});
+
+module.exports = AlterTableQuery.reopenClass({
+  __name__: 'AlterTableQuery'
+});

lib/schema/table/column_alterer.js

@@ -0,0 +1,53 @@
+var ColumnCreator = require('./column_creator');
+var property = require('../../util/property').fn;
+
+/**
+ * A class that can create, drop & alter columns for tables.
+ *
+ * @protected
+ * @constructor ColumnAlterer
+ * @param {Array} columns An empty array that will be mutated to contain
+ * {@link ColumnAlterer~Column} objects as they are created.
+ */
+var ColumnAlterer = ColumnCreator.extend({
+  init: function() {
+    this._super.apply(this, arguments);
+    this._dropped = [];
+  },
+
+  /**
+   * Alias for {@link ColumnCreator#columns}.
+   *
+   * @private
+   * @scope internal
+   * @type {Array.<Column>}
+   * @readonly
+   */
+  added: property({ property: 'columns' }),
+
+  /**
+   * Names of dropped columns.
+   *
+   * @private
+   * @scope internal
+   * @type {Array.<String>}
+   * @readonly
+   */
+  dropped: property(),
+
+  /**
+   * Drop a column.
+   *
+   * @method
+   * @public
+   * @param {String} column The column name.
+   */
+  drop: function(column) {
+    this._dropped.push(column);
+  }
+
+});
+
+module.exports = ColumnAlterer.reopenClass({
+  __name__: 'Table~ColumnAlterer'
+});

lib/schema/table/column_creator.js

@@ -2,6 +2,7 @@
 
 var Class = require('../../util/class');
 var Column = require('./column');
+var property = require('../../util/property').fn;
 
 /**
  * Helper method for defining methods that can create attributable columns that
@@ -31,15 +32,23 @@ var col = function(type) {
  *
  * @protected
  * @constructor ColumnCreator
- * @param {Array} columns An empty array that will be mutated to contain
- * {@link Column} objects as they are created.
  */
 var ColumnCreator = Class.extend({
-  init: function(columns) {
-    this._super();
-    this._columns = columns;
+  init: function() {
+    this._super.apply(this, arguments);
+    this._columns = [];
   },
 
+  /**
+   * Created columns.
+   *
+   * @private
+   * @scope internal
+   * @type {Array.<Column>}
+   * @readonly
+   */
+  columns: property(),
+
   /**
    * Alias for {@link ColumnCreator#serial}.
    *

lib/schema/table/create.js

@@ -29,14 +29,15 @@ var CreateTableQuery = BaseQuery.extend(/** @lends CreateTableQuery# */ {
     if (!cb) { throw new Error('Missing callback to create columns.'); }
     this._super();
     this._name = name;
-    this._columns = [];
+    this._creator = ColumnCreator.create();
     this._options = {
       ifNotExists: false
     };
 
-    cb(ColumnCreator.create(this._columns));
+    cb(this._creator);
 
-    var pkCount = _(this._columns).map('options').filter('primaryKey').size();
+    var pkCount = _(this._creator.columns)
+      .map('options').filter('primaryKey').size();
     if (pkCount > 1) {
       throw new Error('Table may only have one primary key column.');
     }
@@ -52,7 +53,7 @@ var CreateTableQuery = BaseQuery.extend(/** @lends CreateTableQuery# */ {
   _take: function(orig) {
     this._super(orig);
     this._name = orig._name;
-    this._columns = orig._columns;
+    this._creator = orig._creator;
     this._options = _.clone(orig._options);
   },
 
@@ -66,7 +67,7 @@ var CreateTableQuery = BaseQuery.extend(/** @lends CreateTableQuery# */ {
   sql: function() {
     return this._adapter.phrasing.createTable({
       name: this._name,
-      columns: this._columns,
+      columns: this._creator.columns,
       options: this._options
     });
   },