【C#学习——特性】

前言

C#特性学习、主要是用在数据库连接时如何动态创建对应的表，正常开发应该使用如Entity Framework等ORM框架实现自动创建生成。

代码

1、声明特性

[AttributeUsage(AttributeTargets.Property)]
public class PrimaryKeyAttribute : Attribute { }

[AttributeUsage(AttributeTargets.Property)]
public class ForeignKeyAttribute : Attribute
{
    public string ReferenceTable { get; }
    public string ReferenceColumn { get; }

    public ForeignKeyAttribute(string referenceTable, string referenceColumn)
    {
        ReferenceTable = referenceTable;
        ReferenceColumn = referenceColumn;
    }
}

[AttributeUsage(AttributeTargets.Property)]
public class RequiredAttribute : Attribute { }

[AttributeUsage(AttributeTargets.Property)]
public class UniqueAttribute : Attribute { }

2、定义特性方法

//特性方法
public static class AttributeMethod
{
    //反射+泛型打印特性名
    public static void GetAttributies<T>()
    {
        Type objType = typeof(T);
        foreach (var property in objType.GetProperties())
        {
            Console.WriteLine($"Property: {property.Name}");

            if (property.GetCustomAttribute<PrimaryKeyAttribute>() != null)
            {
                Console.WriteLine("  - Primary Key");
            }
            if (property.GetCustomAttribute<ForeignKeyAttribute>() != null)
            {
                var foreignKey = property.GetCustomAttribute<ForeignKeyAttribute>();
                Console.WriteLine($"  - Foreign Key: References {foreignKey.ReferenceTable}.{foreignKey.ReferenceColumn}");
            }
            if (property.GetCustomAttribute<RequiredAttribute>() != null)
            {
                Console.WriteLine("  - Required");
            }
            if (property.GetCustomAttribute<UniqueAttribute>() != null)
            {
                Console.WriteLine("  - Unique");
            }
        }
    }
}

3、创建类并指定特性

public class User
{
    [PrimaryKey]
    public int Id { get; set; }

    [Required]
    [Unique]
    public string Username { get; set; }

    [Required]
    public string Password { get; set; }

    [ForeignKey("Role", "Id")]
    public int RoleId { get; set; }
}

public class Role
{
    [PrimaryKey]
    public int Id { get; set; }

    [Required]
    public string Name { get; set; }
}

调用方法获取并打印特性名

internal class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("输出User特性:");
        AttributeMethod.GetAttributies<User>();
        Console.WriteLine();
        Console.WriteLine("输出Role特性:");
        AttributeMethod.GetAttributies<Role>();
        
        Console.ReadKey();
        
    }
}

结果