Discover the compiled model automatically

src/EFCore.Design/Properties/DesignStrings.resx

@@ -160,7 +160,7 @@
     <value>The entity type '{entityType}' has a defining query configured. Compiled model can't be generated, because defining queries are not supported.</value>
   </data>
   <data name="CompiledModelGenerated" xml:space="preserve">
-    <value>Successfully generated a compiled model, to use it call '{optionsCall}'. Run this command again when the model is modified.</value>
+    <value>Successfully generated a compiled model, it will be discovered automatically, but you can also call '{optionsCall}'. Run this command again when the model is modified.</value>
   </data>
   <data name="CompiledModelQueryFilter" xml:space="preserve">
     <value>The entity type '{entityType}' has a query filter configured. Compiled model can't be generated, because query filters are not supported.</value>

src/EFCore.Design/Scaffolding/Internal/CSharpRuntimeModelCodeGenerator.cs

@@ -22,6 +22,7 @@ public class CSharpRuntimeModelCodeGenerator : ICompiledModelCodeGenerator
     private readonly ICSharpRuntimeAnnotationCodeGenerator _annotationCodeGenerator;
 
     private const string FileExtension = ".cs";
+    private const string AssemblyAttributesSuffix = "AssemblyAttributes";
     private const string ModelSuffix = "Model";
     private const string ModelBuilderSuffix = "ModelBuilder";
     private const string EntityTypeSuffix = "EntityType";
@@ -62,6 +63,11 @@ public virtual IReadOnlyCollection<ScaffoldedFile> GenerateModel(
         // Translated expressions don't have nullability annotations
         var nullable = false;
         var scaffoldedFiles = new List<ScaffoldedFile>();
+
+        var assemblyAttributesCode = CreateAssemblyAttributes(options.ModelNamespace, options.ContextType, nullable);
+        var assemblyInfoFileName = options.ContextType.ShortDisplayName() + AssemblyAttributesSuffix + FileExtension;
+        scaffoldedFiles.Add(new ScaffoldedFile { Path = assemblyInfoFileName, Code = assemblyAttributesCode });
+
         var modelCode = CreateModel(options.ModelNamespace, options.ContextType, nullable);
         var modelFileName = options.ContextType.ShortDisplayName() + ModelSuffix + FileExtension;
         scaffoldedFiles.Add(new ScaffoldedFile { Path = modelFileName, Code = modelCode });
@@ -118,6 +124,29 @@ private static string GenerateHeader(SortedSet<string> namespaces, string curren
         return builder.ToString();
     }
 
+    private string CreateAssemblyAttributes(
+        string @namespace,
+        Type contextType,
+        bool nullable)
+    {
+        var mainBuilder = new IndentedStringBuilder();
+        var namespaces = new SortedSet<string>(new NamespaceComparer())
+        {
+            typeof(DbContextModelAttribute).Namespace!,
+            @namespace
+        };
+
+        AddNamespace(contextType, namespaces);
+
+        mainBuilder
+            .Append("[assembly: DbContextModel(typeof(").Append(_code.Reference(contextType))
+            .Append("), typeof(").Append(GetModelClassName(contextType)).AppendLine("))]");
+
+        return GenerateHeader(namespaces, currentNamespace: "", nullable) + mainBuilder;
+    }
+
+    private string GetModelClassName(Type contextType) => _code.Identifier(contextType.ShortDisplayName()) + ModelSuffix;
+
     private string CreateModel(
         string @namespace,
         Type contextType,
@@ -139,7 +168,7 @@ private string CreateModel(
             mainBuilder.Indent();
         }
 
-        var className = _code.Identifier(contextType.ShortDisplayName()) + ModelSuffix;
+        var className = GetModelClassName(contextType);
         mainBuilder
             .Append("[DbContext(typeof(").Append(_code.Reference(contextType)).AppendLine("))]")
             .Append("public partial class ").Append(className).AppendLine(" : " + nameof(RuntimeModel))
@@ -222,7 +251,7 @@ private string CreateModelBuilder(
             mainBuilder.Indent();
         }
 
-        var className = _code.Identifier(contextType.ShortDisplayName()) + ModelSuffix;
+        var className = GetModelClassName(contextType);
         mainBuilder
             .Append("public partial class ").AppendLine(className)
             .AppendLine("{");

src/EFCore/Infrastructure/DbContextModelAttribute.cs

@@ -0,0 +1,42 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.EntityFrameworkCore.Infrastructure;
+
+/// <summary>
+///     Identifies the <see cref="RuntimeModel" /> implementation that should be used for a given context.
+/// </summary>
+/// <remarks>
+///     <para>
+///         This attribute will usually be generated with the compiled model and doesn't need to be specified in your code.
+///     </para>
+///     <para>
+///         See <see href="https://aka.ms/efcore-docs-dbcontext-pooling">Using DbContext pooling</see> for more information and examples.
+///     </para>
+/// </remarks>
+[AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
+public sealed class DbContextModelAttribute : Attribute
+{
+    /// <summary>
+    ///     Initializes a new instance of the <see cref="DbContextAttribute" /> class.
+    /// </summary>
+    /// <param name="contextType">The associated context.</param>
+    /// <param name="modelType">The compiled model.</param>
+    public DbContextModelAttribute(Type contextType, Type modelType)
+    {
+        Check.NotNull(contextType, nameof(contextType));
+
+        ContextType = contextType;
+        ModelType = modelType;
+    }
+
+    /// <summary>
+    ///     Gets the associated context.
+    /// </summary>
+    public Type ContextType { get; }
+
+    /// <summary>
+    ///     Gets the compiled model.
+    /// </summary>
+    public Type ModelType { get; }
+}

src/EFCore/Internal/DbContextServices.cs

@@ -68,7 +68,7 @@ private IModel CreateModel(bool designTime)
             _inOnModelCreating = true;
 
             var dependencies = _scopedProvider!.GetRequiredService<ModelCreationDependencies>();
-            var modelFromOptions = CoreOptions?.Model;
+            var modelFromOptions = CoreOptions?.Model ?? FindCompiledModel(_currentContext!.Context.GetType());
 
             var modelVersion = modelFromOptions?.GetProductVersion();
             if (modelVersion != null)
@@ -88,13 +88,45 @@ private IModel CreateModel(bool designTime)
                 || (designTime && modelFromOptions is not Metadata.Internal.Model)
                     ? RuntimeFeature.IsDynamicCodeSupported
                         ? dependencies.ModelSource.GetModel(_currentContext!.Context, dependencies, designTime)
-                        : throw new InvalidOperationException(CoreStrings.NativeAotNoCompiledModel)
+                        : throw new InvalidOperationException(CoreStrings.NativeAotDesignTimeModel)
                     : dependencies.ModelRuntimeInitializer.Initialize(modelFromOptions, designTime, dependencies.ValidationLogger);
         }
         finally
         {
             _inOnModelCreating = false;
         }
+
+        static IModel? FindCompiledModel(Type contextType)
+        {
+            var contextAssembly = contextType.Assembly;
+            IModel? model = null;
+            foreach (var modelAttribute in contextAssembly.GetCustomAttributes<DbContextModelAttribute>())
+            {
+                if (modelAttribute.ContextType != contextType)
+                {
+                    continue;
+                }
+
+                var modelType = modelAttribute.ModelType;
+
+                var instanceProperty = modelType.GetProperty("Instance", BindingFlags.Public | BindingFlags.Static);
+                if (instanceProperty == null
+                    || instanceProperty.PropertyType != typeof(IModel))
+                {
+                    throw new InvalidOperationException(CoreStrings.CompiledModelMissingInstance(modelType.DisplayName()));
+                }
+
+                if (model != null)
+                {
+                    throw new InvalidOperationException(CoreStrings.CompiledModelDuplicateAttribute(
+                        contextAssembly.FullName, contextType.DisplayName()));
+                }
+
+                model = (IModel)instanceProperty.GetValue(null)!;
+            }
+
+            return model;
+        }
     }
 
     /// <summary>

src/EFCore/Properties/CoreStrings.resx

@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
 <root>
-  <!--
-    Microsoft ResX Schema
-
+  <!-- 
+    Microsoft ResX Schema 
+    
     Version 2.0
-
-    The primary goals of this format is to allow a simple XML format
-    that is mostly human readable. The generation and parsing of the
-    various data types are done through the TypeConverter classes
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
     associated with the data types.
-
+    
     Example:
-
+    
     ... ado.net/XML headers & schema ...
     <resheader name="resmimetype">text/microsoft-resx</resheader>
     <resheader name="version">2.0</resheader>
@@ -26,36 +26,36 @@
         <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
         <comment>This is a comment</comment>
     </data>
-
-    There are any number of "resheader" rows that contain simple
+                
+    There are any number of "resheader" rows that contain simple 
     name/value pairs.
-
-    Each data row contains a name, and value. The row also contains a
-    type or mimetype. Type corresponds to a .NET class that support
-    text/value conversion through the TypeConverter architecture.
-    Classes that don't support this are serialized and stored with the
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
     mimetype set.
-
-    The mimetype is used for serialized objects, and tells the
-    ResXResourceReader how to depersist the object. This is currently not
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
     extensible. For a given mimetype the value must be set accordingly:
-
-    Note - application/x-microsoft.net.object.binary.base64 is the format
-    that the ResXResourceWriter will generate, however the reader can
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
     read any of the formats listed below.
-
+    
     mimetype: application/x-microsoft.net.object.binary.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
             : and then encoded with base64 encoding.
-
+    
     mimetype: application/x-microsoft.net.object.soap.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
             : and then encoded with base64 encoding.
 
     mimetype: application/x-microsoft.net.object.bytearray.base64
-    value   : The object must be serialized into a byte array
+    value   : The object must be serialized into a byte array 
             : using a System.ComponentModel.TypeConverter
             : and then encoded with base64 encoding.
     -->
@@ -288,9 +288,15 @@
   <data name="ComparerPropertyMismatchElement" xml:space="preserve">
     <value>The comparer for element type '{type}' cannot be used for '{entityType}.{propertyName}' because its element type is '{elementType}'.</value>
   </data>
+  <data name="CompiledModelDuplicateAttribute" xml:space="preserve">
+    <value>More than a single DbContextModelAttribute was found in the assembly '{assemblyName}' corresponding to the context type '{contextType}'</value>
+  </data>
   <data name="CompiledModelIncompatibleTypeMapping" xml:space="preserve">
     <value>The type mapping used is incompatible with a compiled model. The mapping type must have a 'public static readonly {typeMapping} {typeMapping}.Default' property.</value>
   </data>
+  <data name="CompiledModelMissingInstance" xml:space="preserve">
+    <value>'{modelType}' must declare a static property named 'Instance' that returns 'IModel'.</value>
+  </data>
   <data name="CompiledQueryDifferentModel" xml:space="preserve">
     <value>The compiled query '{queryExpression}' was executed with a different model than it was compiled against. Compiled queries can only be used with a single model.</value>
   </data>
@@ -1156,6 +1162,9 @@
   <data name="NamedIndexWrongType" xml:space="preserve">
     <value>The index with name {indexName} cannot be removed from the entity type '{entityType}' because no such index exists on that entity type.</value>
   </data>
+  <data name="NativeAotDesignTimeModel" xml:space="preserve">
+    <value>Design-time DbContext operations are not supported when publishing with NativeAOT.</value>
+  </data>
   <data name="NativeAotNoCompiledModel" xml:space="preserve">
     <value>Model building is not supported when publishing with NativeAOT. Use a compiled model.</value>
   </data>

test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/Basic_cosmos_model/DbContextAssemblyAttributes.cs

@@ -0,0 +1,9 @@
+// <auto-generated />
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using TestNamespace;
+
+#pragma warning disable 219, 612, 618
+#nullable disable
+
+[assembly: DbContextModel(typeof(DbContext), typeof(DbContextModel))]

test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/SimpleModel/DbContextAssemblyAttributes.cs

@@ -0,0 +1,9 @@
+// <auto-generated />
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using TestNamespace;
+
+#pragma warning disable 219, 612, 618
+#nullable disable
+
+[assembly: DbContextModel(typeof(DbContext), typeof(DbContextModel))]

test/EFCore.Cosmos.FunctionalTests/Scaffolding/Baselines/SimpleModel/DbContextModelBuilder.cs

@@ -0,0 +1,27 @@
+// <auto-generated />
+using System;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Metadata;
+
+#pragma warning disable 219, 612, 618
+#nullable disable
+
+namespace TestNamespace
+{
+    public partial class DbContextModel
+    {
+        private DbContextModel()
+            : base(skipDetectChanges: false, modelId: new Guid("00000000-0000-0000-0000-000000000000"), entityTypeCount: 1)
+        {
+        }
+
+        partial void Initialize()
+        {
+            var dependentDerived = DependentDerivedEntityType.Create(this);
+
+            DependentDerivedEntityType.CreateAnnotations(dependentDerived);
+
+            AddAnnotation("Cosmos:ContainerName", "DbContext");
+        }
+    }
+}