[EF] - 动态创建模型：System.Reflection.Emit + Code First

动态创建Entity Framework模型并且创建数据库

使用System.Reflection.Emit+Code First model创建以下的一个实体类和DbContext并且创建数据库:

 1 using System;
 2
 3 public class Blog
 4
 5 {
 6
 7 private int id;
 8
 9 private string name;
10
11 public int ID
12
13 {
14
15 get
16
17 {
18
19 return this.id;
20
21 }
22
23 set
24
25 {
26
27 this.id = value;
28
29 }
30
31 }
32
33 public string Name
34
35 {
36
37 get
38
39 {
40
41 return this.name;
42
43 }
44
45 set
46
47 {
48
49 this.name = value;
50
51 }
52
53 }
54
55 }

using System;

using System.Data.Entity;

public class Sample20141106 : DbContext

{

private DbSet<Blog> blogs;

public DbSet<Blog> Blogs

{

get

{

return this.blogs;

}

set

{

this.blogs = value;

}

}

}

1.创建类所在的程序集合module:

AppDomain myDomain = Thread.GetDomain();

AssemblyName myAsmName = new AssemblyName();

myAsmName.Name = "Sample20141106";

// To generate a persistable assembly, specify AssemblyBuilderAccess.RunAndSave.

ssemblyBuilder myAsmBuilder = myDomain.DefineDynamicAssembly(myAsmName, AssemblyBuilderAccess.RunAndSave);

// Generate a persistable single-module assembly.

ModuleBuilder myModBuilder = myAsmBuilder.DefineDynamicModule(myAsmName.Name, myAsmName.Name + ".dll");

2.创建Blog实体类:

创建类型:

TypeBuilder BlogTypeBuilder = myModBuilder.DefineType("Blog", TypeAttributes.Public);

创建ID和Name properties:（这个应该可以考虑写成同样方法，传入类型和类型名称）

FieldBuilder idBldr = BlogTypeBuilder.DefineField("id", typeof(int), FieldAttributes.Private);

            FieldBuilder nameBldr = BlogTypeBuilder.DefineField("name", typeof(string), FieldAttributes.Private);

            PropertyBuilder idPropBldr = BlogTypeBuilder.DefineProperty("ID", PropertyAttributes.HasDefault, typeof(int), null);

            PropertyBuilder namePropBldr = BlogTypeBuilder.DefineProperty("Name", PropertyAttributes.HasDefault, typeof(string), null);

            MethodAttributes getSetAttr = MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig;

            MethodBuilder idGetPropMthdBldr = BlogTypeBuilder.DefineMethod("get_ID", getSetAttr, typeof(int), Type.EmptyTypes);

            ILGenerator idGetIL = idGetPropMthdBldr.GetILGenerator();

            idGetIL.Emit(OpCodes.Ldarg_0);

            idGetIL.Emit(OpCodes.Ldfld, idBldr);

            idGetIL.Emit(OpCodes.Ret);

            MethodBuilder idSetPropMthdBldr = BlogTypeBuilder.DefineMethod("set_ID", getSetAttr, null, new Type[] { typeof(int) });

            ILGenerator idSetIL = idSetPropMthdBldr.GetILGenerator();

            idSetIL.Emit(OpCodes.Ldarg_0);

            idSetIL.Emit(OpCodes.Ldarg_1);

            idSetIL.Emit(OpCodes.Stfld, idBldr);

            idSetIL.Emit(OpCodes.Ret);

            idPropBldr.SetGetMethod(idGetPropMthdBldr);

            idPropBldr.SetSetMethod(idSetPropMthdBldr);

            MethodBuilder nameGetPropMthdBldr = BlogTypeBuilder.DefineMethod("get_Name", getSetAttr, typeof(int), Type.EmptyTypes);

            ILGenerator nameGetIL = nameGetPropMthdBldr.GetILGenerator();

            nameGetIL.Emit(OpCodes.Ldarg_0);

            nameGetIL.Emit(OpCodes.Ldfld, nameBldr);

            nameGetIL.Emit(OpCodes.Ret);

            MethodBuilder nameSetPropMthdBldr = BlogTypeBuilder.DefineMethod("set_Name", getSetAttr, null, new Type[] { typeof(int) });

            ILGenerator nameSetIL = nameSetPropMthdBldr.GetILGenerator();

            nameSetIL.Emit(OpCodes.Ldarg_0);

            nameSetIL.Emit(OpCodes.Ldarg_1);

            nameSetIL.Emit(OpCodes.Stfld, nameBldr);

            nameSetIL.Emit(OpCodes.Ret);

            namePropBldr.SetGetMethod(nameGetPropMthdBldr);

            namePropBldr.SetSetMethod(nameSetPropMthdBldr);

生成类型到内存中,这个类型在后面生成DbContext有用

 Type blogType = BlogTypeBuilder.CreateType();

2.创建DbContxt类型:

构造类型:

TypeBuilder Sample20141106TypeBuilder = myModBuilder.DefineType("Sample20141106", TypeAttributes.Public);

Sample20141106TypeBuilder.SetParent(typeof(DbContext));//生成的类型继承DbContext, 在生成程序集的时候会自动引用EntiyFrame.dll.

构造DbSet<T>属性:

FieldBuilder blogFieldBuilder = Sample20141106TypeBuilder.DefineField("blogs", typeof(DbSet<>).MakeGenericType(blogType), FieldAttributes.Private);

            PropertyBuilder blogPropBldr = Sample20141106TypeBuilder.DefineProperty("Blogs", PropertyAttributes.HasDefault, typeof(DbSet<>).MakeGenericType(blogType), null);

            MethodBuilder blogGetPropMthdBldr = Sample20141106TypeBuilder.DefineMethod("get_Blog", getSetAttr, typeof(DbSet<>).MakeGenericType(blogType), Type.EmptyTypes);

            ILGenerator blogGetIL = blogGetPropMthdBldr.GetILGenerator();

            blogGetIL.Emit(OpCodes.Ldarg_0);

            blogGetIL.Emit(OpCodes.Ldfld, blogFieldBuilder);

            blogGetIL.Emit(OpCodes.Ret);

            MethodBuilder blogSetPropMthdBldr = Sample20141106TypeBuilder.DefineMethod("set_Blog", getSetAttr, null, new Type[] { typeof(DbSet<>).MakeGenericType(blogType) });

            ILGenerator blogSetIL = blogSetPropMthdBldr.GetILGenerator();

            blogSetIL.Emit(OpCodes.Ldarg_0);

            blogSetIL.Emit(OpCodes.Ldarg_1);

            blogSetIL.Emit(OpCodes.Stfld, blogFieldBuilder);

            blogSetIL.Emit(OpCodes.Ret);

            blogPropBldr.SetGetMethod(blogGetPropMthdBldr);

            blogPropBldr.SetSetMethod(blogSetPropMthdBldr);

生成DbContext类型到内存:

Type Sample20141106Type = Sample20141106TypeBuilder.CreateType();

可以选择将模型保存到dll中:

 myAsmBuilder.Save(myAsmName.Name + ".dll");

然后可以在其他project中引用。或者用反射直接生成数据库:

Type Sample20141106 = BuildDynamicTypeWithProperties();

object db = Activator.CreateInstance(Sample20141106);

Type Database = Sample20141106.GetProperty("Database").GetValue(db).GetType();

object database = Sample20141106.GetProperty("Database").GetValue(db);

MethodInfo CreateIfNotExists = Database.GetMethod("CreateIfNotExists");

CreateIfNotExists.Invoke(database, null);