在EF代码中首先是否存在描述字段的数据注释？

Question

在MS-SQL中设计表格时，您可以选择为添加到表格的每个列添加description。 EF Code First在Data Annotations的帮助下可以做到吗？

Answer 1

您使用我的soultion请阅读一点点前：

扩展属性：
https://technet.microsoft.com/en-us/library/ms190243(v=sql.105).aspx

属性：
http://www.dotnetperls.com/attribute

我的解决方案将允许你为任何类似的财产做一个阴影描述：

[Description("My Column description!")] 
public string RegionCity { get; set; } 

注：

• 复制粘贴soultion，一切都应该作品（donnot忘记在app.config连接字符串）！
• 您可以使用sql命令IF NOT EXISTS来检查扩展属性是否已经存在。

• 您可以构建自己的通用逻辑或C＃扩展来读取任何属性的descirption，这应该很容易只是添加了一个字符串示例。

  using System; 
  using System.Linq; 
  
  namespace EntityFrameworkDemo 
  { 
  using System.Data.Entity; 
  
  public class Program 
  { 
      public static void Main() 
      { 
       Database.SetInitializer(new DropCreateDatabaseAlways<MyDbContext>()); 
  
  
       using (var myDbContext = new MyDbContext("DefaultConnection")) 
       { 
        // Maybe you do not need this line! 
        myDbContext.Database.Initialize(true); 
  
        // Adding one time or use the IF NOT EXISTS SQL Command! 
        var c = new ColumnsDescription(); 
        c.AddColumnsDescriptions(myDbContext); 
  
        var region = new Region { RegionCity = "Test 1", RegionSeconcdCity = "Test2" }; 
        myDbContext.Regions.Add(region); 
        myDbContext.SaveChanges(); 
       } 
  
  
       // Reading the extended properties 
       using (var myDbContext = new MyDbContext("DefaultConnection")) 
       { 
        var ep = "select value from fn_listextendedproperty('MS_Description','schema','dbo','table', 'Regions', 'column', 'RegionCity');"; 
  
        // For example you can read your extend property like following or you make a generic reader 
        var properties = myDbContext.Database.SqlQuery<string>(ep).First(); 
  
        Console.WriteLine(properties); 
       } 
      } 
  
      [AttributeUsage(AttributeTargets.Property)] 
      public class DescriptionAttribute : Attribute 
      { 
       string value; 
  
       public DescriptionAttribute(string id) 
       { 
        this.value = id; 
       } 
  
       public string Value 
       { 
        get { return this.value; } 
       } 
      } 
  
      public class ColumnsDescription 
      { 
       public void AddColumnsDescriptions(DbContext mydbContext) 
       { 
        // Fetch all the DbContext class public properties which contains your attributes 
        var dbContextProperies = typeof(DbContext).GetProperties().Select(pi => pi.Name).ToList(); 
  
        // Loop each DbSets of type T 
        foreach (var item in typeof(MyDbContext).GetProperties() 
         .Where(p => dbContextProperies.IndexOf(p.Name) < 0) 
         .Select(p => p)) 
        { 
         if (!item.PropertyType.GetGenericArguments().Any()) 
         { 
          continue; 
         } 
  
         // Fetch the type of "T" 
         var entityModelType = item.PropertyType.GetGenericArguments()[0]; 
         var descriptionInfos = from prop in entityModelType.GetProperties() 
               where prop.GetCustomAttributes(typeof(DescriptionAttribute), true).Any() 
               select new { ColumnName = prop.Name, Attributes = prop.CustomAttributes }; 
  
         foreach (var descriptionInfo in descriptionInfos) 
         { 
          // Sql to create the description column and adding 
          var addDiscriptionColumnSql = 
           @"sp_addextendedproperty @name = N'MS_Description', @value = '" 
           + descriptionInfo.Attributes.First().ConstructorArguments.First() 
           + @"', @level0type = N'Schema', @level0name = dbo, @level1type = N'Table', @level1name = " 
           + entityModelType.Name + "s" + ", @level2type = N'Column', @level2name =" 
           + descriptionInfo.ColumnName; 
  
          var sqlCommandResult = mydbContext.Database.ExecuteSqlCommand(addDiscriptionColumnSql); 
         } 
        } 
       } 
      } 
  
      public class Region 
      { 
       public int Id { get; set; } 
  
       [Description("My Column description!")] 
       public string RegionCity { get; set; } 
  
       [Description("My Second Column description!")] 
       public string RegionSeconcdCity { get; set; } 
  
      } 
  
      public class MyDbContext : DbContext 
      { 
       public DbSet<Region> Regions { get; set; } 
  
       public MyDbContext(string connectionString) 
        : base("name=" + connectionString) 
       { 
       } 
      } 
  } 
  }