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

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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);