Add more model building breaking changes.

entity-framework/core/what-is-new/ef-core-5.0/breaking-changes.md

@@ -24,8 +24,11 @@ The following API and behavior changes have the potential to break existing appl
 | [Cosmos: GetPropertyName and SetPropertyName were renamed](#cosmos-metadata)                                                          | Low        |
 | [Value generators are called when the entity state is changed from Detached to Unchanged, Updated, or Deleted](#non-added-generation) | Low        |
 | [IMigrationsModelDiffer now uses IRelationalModel](#relational-model)                                                                 | Low        |
+| [ToView() is treated differently by migrations](#toview)                                                                              | Low        |
+| [ToTable(null) marks the entity type as not mapped to a table](#totable)                                                              | Low        |
 | [Discriminators are read-only](#read-only-discriminators)                                                                             | Low        |
 | [Provider-specific EF.Functions methods throw for InMemory provider](#no-client-methods)                                              | Low        |
+| [IProperty.GetColumnName() is now obsolete](#getcolumnname-obsolete)                                                                  | Low        |
 | [IndexBuilder.HasName is now obsolete](#index-obsolete)                                                                               | Low        |
 | [A pluralizer is now included for scaffolding reverse engineered models](#pluralizer)                                                 | Low        |
 | [INavigationBase replaces INavigation in some APIs to support skip navigations](#inavigationbase)                                     | Low        |
@@ -335,6 +338,64 @@ var hasDifferences = modelDiffer.HasDifferences(
 
 We are planning to improve this experience in 6.0 ([see #22031](https://github.com/dotnet/efcore/issues/22031))
 
+<a name="toview"></a>
+
+### ToView() is treated differently by migrations
+
+[Tracking Issue #2725](https://github.com/dotnet/efcore/issues/2725)
+
+#### Old behavior
+
+Calling `ToView(string)` made the migrations ignore the entity type in addition to mapping it to a view.
+
+#### New behavior
+
+Now `ToView(string)` marks the entity type as not mapped to a table in addition to mapping it to a view. This results in the first migration after upgrading to EF Core 5 to try to drop the default table for this entity type as it's not longer ignored.
+
+#### Why
+
+EF Core now allows an entity type to be mapped to both a table and a view simultaneously, so `ToView` is no longer a valid indicator that it should be ignored by migrations.
+
+#### Mitigations
+
+Use the following code to mark the mapped table as excluded from migrations:
+
+```csharp
+protected override void OnModelCreating(ModelBuilder modelBuilder)
+{
+    modelBuilder.Entity<User>().ToTable("UserView", t => t.ExcludeFromMigrations());
+}
+```
+
+<a name="totable"></a>
+
+### ToTable(null) marks the entity type as not mapped to a table
+
+[Tracking Issue #21172](https://github.com/dotnet/efcore/issues/21172)
+
+#### Old behavior
+
+`ToTable(null)` would reset the table name to the default.
+
+#### New behavior
+
+`ToTable(null)` now marks the entity type as not mapped to any table.
+
+#### Why
+
+EF Core now allows an entity type to be mapped to both a table and a view simultaneously, so `ToTable(null)` is used to indicate that it isn't mapped to any table.
+
+#### Mitigations
+
+Use the following code to reset the table name to the default if it's not mapped to a view or a DbFunction:
+
+```csharp
+protected override void OnModelCreating(ModelBuilder modelBuilder)
+{
+    modelBuilder.Entity<User>().Metadata.RemoveAnnotation(RelationalAnnotationNames.TableName);
+}
+```
+
 <a name="read-only-discriminators"></a>
 
 ### Discriminators are read-only
@@ -385,6 +446,32 @@ Provider-specific methods map to a database function. The computation done by th
 
 Since there's no way to mimic behavior of database functions accurately, you should test the queries containing them against same kind of database as in production.
 
+<a name="getcolumnname-obsolete"></a>
+
+### IProperty.GetColumnName() is now obsolete
+
+[Tracking Issue #2266](https://github.com/dotnet/efcore/issues/2266)
+
+#### Old behavior
+
+`GetColumnName()` returned the name of the column that a property is mapped to.
+
+#### New behavior
+
+`GetColumnName()` still returns of a column that a property is mapped to, but this behavior is now ambiguous since EF Core 5 supports TPT and simultaneous mapping to a view or a function where these mappings could use different column names for the same property.
+
+#### Why
+
+We marked this method as obsolete to guide users to a more accurate overload - `IProperty.GetColumnName(StoreObjectIdentifier)`.
+
+#### Mitigations
+
+Use the following code to get the column name for a specific table:
+
+```csharp
+var columnName = property.GetColumnName(StoreObjectIdentifier.Table("Users", null)));
+```
+
 <a name="index-obsolete"></a>
 
 ### IndexBuilder.HasName is now obsolete