Entity Framework Tutorial Basics（40）：Validate Entity-优快云博客

本文介绍如何为Entity Framework中的实体自定义服务器端验证。通过重写DBContext的ValidateEntity方法，可以实现对特定实体属性的检查。例如，对于学生实体，如果姓名为空，则会抛出验证异常。

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Validate Entity

You can write custom server side validation for any entity. To accomplish this, override ValidateEntity method of DBContext as shown below.

protected override System.Data.Entity.Validation.DbEntityValidationResult ValidateEntity(DbEntityEntry entityEntry, System.Collections.Generic.IDictionary<object, object> items)
{
    if (entityEntry.Entity is Student)
    {
        if (entityEntry.CurrentValues.GetValue<string>("StudentName") == "")
        {
            var list = new List<System.Data.Entity.Validation.DbValidationError>();
            list.Add(new System.Data.Entity.Validation.DbValidationError("StudentName", "StudentName is required"));

            return new System.Data.Entity.Validation.DbEntityValidationResult(entityEntry, list);
        }
    }
    return base.ValidateEntity(entityEntry, items);
}

As you can see in the above code, we are validating the Student entity. If StudentName is blank, then we are adding DBValidationError into DBEntityValidationResult. So whenever you call DBContext.SaveChanges method and you try to save Student entity without StudentName, then it will throw DbEntityValidationException. For example:

try
{
    using (var ctx = new SchoolDBEntities())
    {
        ctx.Students.Add(new Student() { StudentName = "" });
        ctx.Standards.Add(new Standard() { StandardName = "" });

        ctx.SaveChanges();
    }
}
catch (DbEntityValidationException dbEx)
{
    foreach (DbEntityValidationResult entityErr in dbEx.EntityValidationErrors)
    {
        foreach (DbValidationError error in entityErr.ValidationErrors)
        {
            Console.WriteLine("Error Property Name {0} : Error Message: {1}",
                                error.PropertyName, error.ErrorMessage);
        }
    }
}