Move sequences modeling page out of relational and clean up

Part of #1669

Author: roji

.openpublishing.redirection.json

@@ -289,6 +289,11 @@
             "source_path": "entity-framework/core/modeling/relational/unique-constraints.md",
             "redirect_url": "/ef/core/modeling/keys",
             "redirect_document_id": false
+        },
+        {
+            "source_path": "entity-framework/core/modeling/relational/sequences.md",
+            "redirect_url": "/ef/core/modeling/sequences",
+            "redirect_document_id": false
         }
     ]
 }

entity-framework/core/modeling/relational/sequences.md

@@ -0,0 +1,27 @@
+---
+title: Sequences - EF Core
+author: roji
+ms.date: 12/18/2019
+ms.assetid: 94f81a92-3c72-4e14-912a-f99310374e42
+uid: core/modeling/sequences
+---
+# Sequences
+
+> [!NOTE]  
+> Sequences are a feature typically supported only by relational databases. If you're using a non-relational database such as Cosmos, check your database documentation on generating unique values.
+
+A sequence generates unique, sequential numeric values in the database. Sequences are not associated with a specific table, and multiple tables can be set up to draw values from the same sequence.
+
+## Basic usage
+
+You can set up a sequence in the model, and then use it to generate values for properties:
+
+[!code-csharp[Main](../../../samples/core/Modeling/FluentAPI/Sequence.cs?name=Sequence&highlight=3,7)]
+
+Note that the specific SQL used to generate a value from a sequence is database-specific; the above example works on SQL Server but will fail on other databases. Consult your specific database's documentation for more information.
+
+## Configuring sequence settings
+
+You can also configure additional aspects of the sequence, such as its schema, start value, increment, etc.:
+
+[!code-csharp[Main](../../../samples/core/Modeling/FluentAPI/SequenceConfiguration.cs?name=SequenceConfiguration&highlight=3-5)]

entity-framework/core/modeling/sequences.md

@@ -97,6 +97,8 @@
         href: core/modeling/indexes.md
       - name: Inheritance
         href: core/modeling/inheritance.md
+      - name: Sequences
+        href: core/modeling/sequences.md
       - name: Backing Fields
         href: core/modeling/backing-field.md
       - name: Value Conversions
@@ -122,8 +124,6 @@
           href: core/modeling/relational/index.md
         - name: Computed Columns
           href: core/modeling/relational/computed-columns.md
-        - name: Sequences
-          href: core/modeling/relational/sequences.md
         - name: Default Values
           href: core/modeling/relational/default-values.md
         - name: Inheritance (Relational Database)

entity-framework/toc.yml

@@ -2,15 +2,20 @@
 
 namespace EFModeling.FluentAPI.Relational.Sequence
 {
-    #region Model
     class MyContext : DbContext
     {
         public DbSet<Order> Orders { get; set; }
 
+        #region Sequence
         protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
             modelBuilder.HasSequence<int>("OrderNumbers");
+
+            modelBuilder.Entity<Order>()
+                .Property(o => o.OrderNo)
+                .HasDefaultValueSql("NEXT VALUE FOR shared.OrderNumbers");
         }
+        #endregion
     }
 
     public class Order
@@ -19,5 +24,4 @@ public class Order
         public int OrderNo { get; set; }
         public string Url { get; set; }
     }
-    #endregion
 }

samples/core/Modeling/FluentAPI/Relational/SequenceUsed.cs

@@ -1,20 +1,20 @@
 using Microsoft.EntityFrameworkCore;
 
-namespace EFModeling.FluentAPI.Relational.SequenceConfigured
+namespace EFModeling.FluentAPI.Relational.SequenceConfiguration
 {
-    #region Sequence
     class MyContext : DbContext
     {
         public DbSet<Order> Orders { get; set; }
 
+        #region SequenceConfiguration
         protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
             modelBuilder.HasSequence<int>("OrderNumbers", schema: "shared")
                 .StartsAt(1000)
                 .IncrementsBy(5);
         }
+        #endregion
     }   
-    #endregion
 
     public class Order
     {