如何在C#和DataAnnotation中创建通用的UniqueValidationAttribute？

Question

我正在尝试创建一个UniqueAttribute使用System.ComponentModel.DataAnnotations.ValidationAttribute

我希望这是通用的,因为我可以传递Linq DataContext,表名,字段并验证传入值是否唯一.

这是一个不可编译的代码片段,我现在卡在这里:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.DataAnnotations;
using System.Data.Linq;
using System.ComponentModel;

namespace LinkDev.Innovation.Miscellaneous.Validation.Attributes
{
    public class UniqueAttribute : ValidationAttribute
    {
        public string Field { get; set; }

        public override bool IsValid(object value)
        {
            string str = (string)value;
            if (String.IsNullOrEmpty(str))
                return true;

            // this is where I'm stuck
            return (!Table.Where(entity => entity.Field.Equals(str)).Any());           
        }
    }
}

我应该在我的模型中使用它如下:

[Required]
[StringLength(10)]
[Unique(new DataContext(),"Groups","name")]
public string name { get; set; }

编辑:请注意,根据这个:为什么C#禁止通用属性类型？ 我不能使用属性的泛型类型.

所以我的新方法是使用Reflection/Expression树来动态构建Lambda表达式树.

Answer 1

好吧,经过一些搜索后,我偶然发现:http://forums.asp.net/t/1512348.aspx 我想出来了,虽然它涉及到相当多的代码.

用法:

[Required]
[StringLength(10)]
[Unique(typeof(ContactsManagerDataContext),typeof(Group),"name",ErrorMessage="Group already exists")]
public string name { get; set; }

验证码:

public class UniqueAttribute : ValidationAttribute
{
    public Type DataContextType { get; private set; }
    public Type EntityType { get; private set; }
    public string PropertyName { get; private set; }

    public UniqueAttribute(Type dataContextType, Type entityType, string propertyName)
    {
        DataContextType = dataContextType;
        EntityType = entityType;
        PropertyName = propertyName;
    }

    public override bool IsValid(object value)
    {
        string str = (string) value;
        if (String.IsNullOrWhiteSpace(str))
            return true;

        // Cleanup the string
        str = str.Trim();

        // Construct the data context
        ConstructorInfo constructor = DataContextType.GetConstructor(new Type[0]);
        DataContext dataContext = (DataContext)constructor.Invoke(new object[0]);

        // Get the table
        ITable table = dataContext.GetTable(EntityType);

        // Get the property
        PropertyInfo propertyInfo = EntityType.GetProperty(PropertyName);

        // Expression: "entity"
        ParameterExpression parameter = Expression.Parameter(EntityType, "entity");

        // Expression: "entity.PropertyName"
        MemberExpression property = Expression.MakeMemberAccess(parameter, propertyInfo);

        // Expression: "value"
        object convertedValue = Convert.ChangeType(value, propertyInfo.PropertyType);
        ConstantExpression rhs = Expression.Constant(convertedValue);

        // Expression: "entity.PropertyName == value"
        BinaryExpression equal = Expression.Equal(property, rhs);

        // Expression: "entity => entity.PropertyName == value"
        LambdaExpression lambda = Expression.Lambda(equal, parameter);

        // Instantiate the count method with the right TSource (our entity type)
        MethodInfo countMethod = QueryableCountMethod.MakeGenericMethod(EntityType);

        // Execute Count() and say "you're valid if you have none matching"
        int count = (int)countMethod.Invoke(null, new object[] { table, lambda });
        return count == 0;
    }

    // Gets Queryable.Count<TSource>(IQueryable<TSource>, Expression<Func<TSource, bool>>)
    private static MethodInfo QueryableCountMethod = typeof(Queryable).GetMethods().First(m => m.Name == "Count" && m.GetParameters().Length == 2);
}

我不介意它是丑陋的,因为我将它打包在DLL中并重用它,比每个表/字段实现多个UniqueAttribute要好得多.

Answer 2

我编辑了这个..它与 DI 完美配合..:D

public class UniqueAttribute : ValidationAttribute
{
    public UniqueAttribute(Type dataContextType, Type entityType, string propertyName)
    {
        DataContextType = dataContextType;
        EntityType = entityType;
        PropertyName = propertyName;
    }


    public Type DataContextType { get; private set; }


    public Type EntityType { get; private set; }


    public string PropertyName { get; private set; }


    public override bool IsValid(object value)
    {
        // Construct the data context
        //ConstructorInfo constructor = DataContextType.GetConstructor(new Type[0]);
        //DataContext dataContext = (DataContext)constructor.Invoke(new object[0]);
        var repository = DependencyResolver.Current.GetService(DataContextType);
        var data = repository.GetType().InvokeMember("GetAll", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.Public, null, repository, null);

        // Get the table
        //ITable table = dataContext.GetTable(EntityType);


        // Get the property
        PropertyInfo propertyInfo = EntityType.GetProperty(PropertyName);


        // Our ultimate goal is an expression of:
        //   "entity => entity.PropertyName == value"


        // Expression: "value"
        object convertedValue = Convert.ChangeType(value, propertyInfo.PropertyType);
        var rhs = Expression.Constant(convertedValue);


        // Expression: "entity"
        var parameter = Expression.Parameter(EntityType, "entity");


        // Expression: "entity.PropertyName"
        var property = Expression.MakeMemberAccess(parameter, propertyInfo);


        // Expression: "entity.PropertyName == value"
        var equal = Expression.Equal(property, rhs);


        // Expression: "entity => entity.PropertyName == value"
        var lambda = Expression.Lambda(equal, parameter).Compile();

        // Instantiate the count method with the right TSource (our entity type)
        MethodInfo countMethod = QueryableCountMethod.MakeGenericMethod(EntityType);

        // Execute Count() and say "you're valid if you have none matching"
        int count = (int)countMethod.Invoke(null, new object[] { data, lambda });
        return count == 0;
    }


    // Gets Queryable.Count<TSource>(IQueryable<TSource>, Expression<Func<TSource, bool>>)
    //private static MethodInfo QueryableCountMethod = typeof(Enumerable).GetMethods().First(m => m.Name == "Count" && m.GetParameters().Length == 2);
    private static MethodInfo QueryableCountMethod = typeof(System.Linq.Enumerable).GetMethods().Single(
        method => method.Name == "Count" && method.IsStatic && method.GetParameters().Length == 2);
}