前言
我又来啦..
本篇主要记录如何针对CodeFirst做自动添加描述的扩展
为什么要用这个呢.. 因为EF Core3.1 CodeFirst 对于自动添加描述这块 只有少部分的数据库支持..
然而我们的客户大佬们 对这个又有要求..所以..没办法 只能自己扩展~
当然也可以根据这个原理来做一些有意思的扩展~
本文就以不支持的达梦数据库来举个栗子
.(PS:真心希望达梦数据库能开放EF Core相关的源码,这样我们也好提交点贡献,国产数据库还是不能太过敝帚自珍阿..)
正文
1.通过扩展生成器,来实现动态自动添加描述信息
我们知道在SQL Server中,可以通过Fluent API来添加针对表或者字段的描述,如下:
builder.Property(prop.Name)
.HasComment("XXX字段描述");
然而在达梦的上下文中,我们如果这样写..是没任何效果的..不用想,肯定是达梦的开发商没写(很多扩展类都缺斤少两)..
那就需要我们自己扩展了, 所以就少不了翻看EF Core源码..
我们通过翻看源码,可以找到MigrationsSqlGenerator这个类. 类名翻译过来,喔唷,这不就是迁移SQL生成器么
那么我们就需要去实现他啦.首先,我们找到达梦实现他的子类:DmMigrationsSqlGenerator
通过反编译,我们发现,果然他并没实现对于Comment属性的代码,那么我们就需要自行扩展
我们添加MyDmigrationsSqlGenerator类继承DmMigrationsSqlGenerator 添加扩展代码如下:
1 using Microsoft.EntityFrameworkCore.Metadata;
2 using Microsoft.EntityFrameworkCore.Migrations;
3 using Microsoft.EntityFrameworkCore.Migrations.Operations;
4 using System;
5 using System.Collections.Generic;
6 using System.Diagnostics.CodeAnalysis;
7 using System.Linq;
8 using System.Text;
9
10 namespace Ciac.ZTBExpert.Model
11 {
12 public class MyDmigrationsSqlGenerator : DmMigrationsSqlGenerator
13 {
14 public MyDmigrationsSqlGenerator([NotNull] MigrationsSqlGeneratorDependencies dependencies, [NotNull] IMigrationsAnnotationProvider migrationsAnnotations)
15 : base(dependencies, migrationsAnnotations)
16 {
17
18 }
19
20 protected override void Generate(
21 CreateTableOperation operation,
22 IModel model,
23 MigrationCommandListBuilder builder,
24 bool terminate)
25 {
26 base.Generate(operation, model, builder, terminate);
27 var comment = operation.Comment;
28 if (comment != null)
29 {
30 if (terminate)
31 {
32 builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
33 EndStatement(builder);
34 }
35 builder
36 .Append("COMMENT ON TABLE ")
37 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name, operation.Schema))
38 .Append(" IS ")
39 .Append($"'{comment}'")
40 .Append(Dependencies.SqlGenerationHelper.StatementTerminator);
41 }
42 // Comments on the columns
43 foreach (var columnOp in operation.Columns.Where(c => c.Comment != null))
44 {
45 var columnComment = columnOp.Comment;
46 // builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
47 EndStatement(builder);
48 builder
49 .Append("COMMENT ON COLUMN ")
50 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name, operation.Schema))
51 .Append('.')
52 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(columnOp.Name))
53 .Append(" IS ")
54 .Append($"'{columnComment}'")
55 .Append(Dependencies.SqlGenerationHelper.StatementTerminator);
56 }
57 builder.EndCommand();
58 }
59
60
61 protected override void Generate(AlterColumnOperation operation, IModel model, MigrationCommandListBuilder builder)
62 {
63 base.Generate(operation, model, builder);
64 // Comment
65 var oldComment = operation.OldColumn.Comment;
66 var newComment = operation.Comment;
67
68 if (oldComment != newComment)
69 {
70 //builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
71
72 builder
73 .Append("COMMENT ON COLUMN ")
74 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
75 .Append('.')
76 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name))
77 .Append(" IS ")
78 .Append($"'{newComment}'")
79 .Append(Dependencies.SqlGenerationHelper.StatementTerminator);
80 builder.EndCommand();
81 }
82
83 }
84
85 protected override void Generate(AddColumnOperation operation, IModel model, MigrationCommandListBuilder builder, bool terminate)
86 {
87 base.Generate(operation, model, builder, terminate);
88 // Comment
89 var newComment = operation.Comment;
90
91 if (!string.IsNullOrEmpty(newComment))
92 {
93 // builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
94 builder
95 .Append("COMMENT ON COLUMN ")
96 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
97 .Append('.')
98 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name))
99 .Append(" IS ")
100 .Append($"'{newComment}'")
101 .Append(Dependencies.SqlGenerationHelper.StatementTerminator);
102 if (terminate)
103 {
104 EndStatement(builder);
105 }
106 builder.EndCommand();
107
108 }
109
110 }
111 protected override void Generate([NotNull] AlterTableOperation operation, IModel? model, [NotNull] MigrationCommandListBuilder builder)
112 {
113 base.Generate(operation, model, builder);
114 // Comment
115 var oldComment = operation.OldTable.Comment;
116 var newComment = operation.Comment;
117
118 if (oldComment != newComment)
119 {
120
121 EndStatement(builder);
122
123 builder
124 .Append("COMMENT ON TABLE ")
125 .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name, operation.Schema))
126 .Append(" IS ")
127 .Append($"'{newComment}'")
128 .Append(Dependencies.SqlGenerationHelper.StatementTerminator);
129 builder.EndCommand();
130 }
131 }
132 }
133 }
因为我们只是想在创建或者修改表后添加描述.
所以,我们只需要针对CreateTable,AlterColumn,AddColumn,AlterTable 四个生成方法做重写就好了
这样,我们就可以通过在上下文中配置Fluent API就可以自动生成描述了~
我们在EF上下文的OnModelCreating添加代码如下:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<tab_zjcq_ggxx>(a => a.Property("aaa").HasComment("88888"));
}
执行迁移语句Script-Migration
结果如下:
ALTER TABLE "tab_zjcq_ggxx" MODIFY "aaa" NVARCHAR2(50) NULL; /COMMENT ON COLUMN "tab_zjcq_ggxx"."aaa" IS '8888';
2.通过添加Description特性来优化代码风格,方便管理
虽然上面第一步就已经实现了我们的要求,但是我们发现,通过Fluent API 来添加描述,代码可读性会很差,
且一旦表多起来,那么OnModelCreating 方法就会变的超长(虽然也可以写在实体类里面,但是就觉得很麻烦)..
那么能不能像[MaxLength(50)] 这种特性一样,直接在字段上加个特性来解决这个事情呢?~
当然是可以的啦~
我们修改OnModelCreating 中的代码如下:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{ var ddd= modelBuilder.Model.GetEntityTypes().ToList();
foreach (var item in ddd)
{
var tabtype = Type.GetType(item.ClrType.FullName);
var props = tabtype.GetProperties();
var descriptionAttrtable = tabtype.GetCustomAttributes(typeof(DescriptionAttribute), true);
if (descriptionAttrtable.Length > 0)
{
modelBuilder.Entity(item.Name).HasComment(((DescriptionAttribute)descriptionAttrtable[0]).Description);
}
foreach (var prop in props)
{
var descriptionAttr = prop.GetCustomAttributes(typeof(DescriptionAttribute), true);
if (descriptionAttr.Length>0)
{
modelBuilder.Entity(item.Name).Property(prop.Name).HasComment(((DescriptionAttribute)descriptionAttr[0]).Description);
}
}
} }
这里通过反射,得到包含DescriptionAttribute特性的字段,然后读取描述信息,通过HasComment 自动添加~
然后我们给字段添加描述如下:
执行迁移语句Script-Migration~
我们会发现,描述已经自动生成啦~
结束语
其实不管是.NET 5.0 还是EF Core 在开源化的今天,我们只要愿意去多翻翻源码,会发现自己可以扩展的东西还有很多~很多~
最后..在提一嘴,真心希望国产数据库的访问库 能够开源.. 毕竟,人多力量大~
又不需要数据库应用开源..起码访问组件 你能开源吧..
好了..就到这了 瑞思拜~
