add foreign keys and constraints (#1316)

* add foreign keys and constraints

* add property name

src/Microsoft.SqlTools.ServiceLayer/TableDesigner/Contracts/ViewModel/ForeignKeyViewModel.cs

@@ -0,0 +1,34 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Newtonsoft.Json;
+
+namespace Microsoft.SqlTools.ServiceLayer.TableDesigner.Contracts
+{
+    /// <summary>
+    /// The view model of foreign key.
+    /// </summary>
+    public class ForeignKeyViewModel : ObjectViewModelBase
+    {
+        public CheckBoxProperties Enabled { get; set; } = new CheckBoxProperties();
+
+        public DropdownProperties OnDeleteAction { get; set; } = new DropdownProperties();
+
+        public DropdownProperties OnUpdateAction { get; set; } = new DropdownProperties();
+
+        public DropdownProperties PrimaryKeyTable { get; set; } = new DropdownProperties();
+
+        public CheckBoxProperties IsNotForReplication { get; set; } = new CheckBoxProperties();
+
+        public TableComponentProperties<ForeignKeyColumnMapping> Columns { get; set; } = new TableComponentProperties<ForeignKeyColumnMapping>();
+    }
+
+    public class ForeignKeyColumnMapping
+    {
+        public DropdownProperties PrimaryKeyColumn { get; set; } = new DropdownProperties();
+
+        public DropdownProperties ForeignKeyColumn { get; set; } = new DropdownProperties();
+    }
+}