Smark.Data实体默认值描述

在数据设计的时候会针对一些字段设置默认的值，Smark.Data同样支持这样的功能，组件通过在属性中描述一个Value属性来告诉组件这个值如果在没有设置的情况应该提供怎样的值。组件提供一个描述的基类，用户可以根据实际情况的需要扩展出具体的默认值描述，以下是值描述基础类:

    [AttributeUsage(AttributeTargets.Property)]
    public abstract class ValueAttribute:Attribute
    {
        public ValueAttribute(bool afterupdate)
        {
            AfterByUpdate = afterupdate;   
        }
        public bool AfterByUpdate
        {
            get;
            set;
        }
        public virtual void Executing(IConnectinContext cc,object data,PropertyMapper pm,string table)
        {
        }
        public virtual void Executed(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
        }
    }

基础类有两个方法，一个是描述在数据操作前要做的工作，一个是描述数据操作后需要完成的工作。一般设置默认值都在数据操作之前的，为什么还要定义一个操作后的呢。其实有些情况的确要在数据操作后做，如果MSSQL自增ID就是添加后把相关ID值设置到对象中，这个时候就需要在数据操作完成后进行：

    [AttributeUsage(AttributeTargets.Property)]
    public class IDENTITY : ValueAttribute
    {
        public IDENTITY()
            : base(true)
        {
        }
        public override void Executed(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            Command cmd = new Command("select @@IDENTITY ");
            object value = cc.ExecuteScalar(cmd);
            pm.Handler.Set(data,Convert.ChangeType( value,pm.Handler.Property.PropertyType));
        }
    }

如果想给一个属性设置一个默认的GUID值，用于主键可以这样做

    [AttributeUsage(AttributeTargets.Property)]
    public class UID:ValueAttribute
    {
        public UID() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            string uid = Guid.NewGuid().ToString("N");
            pm.Handler.Set(data, uid);
        }
    }

可以通过以下定义引用UID属性

        [ID]
        [UID]
        string EmployeeID { get; set; }

在这基础上可以实现很多需要的默认值，以下是组件内部实现的默认值描述类

    [AttributeUsage(AttributeTargets.Property)]
    public class YearMonth : ValueAttribute
    {
        public YearMonth() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, DateTime.Now.Year.ToString("0000") + DateTime.Now.Month.ToString("00"));
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class Year : ValueAttribute
    {
        public Year() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, DateTime.Now.Year.ToString());
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class Month : ValueAttribute
    {
        public Month() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, DateTime.Now.Month.ToString());
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class Day : ValueAttribute
    {
        public Day() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, DateTime.Now.Day.ToString());
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class NowDate:ValueAttribute
    {
        public NowDate() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, DateTime.Now);
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class DefaultInt : ValueAttribute
    {
        private int mValue = 0;
        public DefaultInt(int value) : base(false) {
            mValue = value;
        }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, mValue);
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class DefaultDecimal : ValueAttribute
    {
        private decimal mValue = 0;
        public DefaultDecimal(string value)
            : base(false)
        {
            mValue = Convert.ToDecimal(value);
        }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data,mValue);
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class DefaultString : ValueAttribute
    { 
        private string mValue = "";
        public DefaultString(string value)
            : base(false)
        {
            mValue = value;
        }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, mValue);
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class DefaultDate:ValueAttribute
    {
        private DateTime mValue = DateTime.MinValue;
        public DefaultDate(string value)
            : base(false)
        {
            mValue =DateTime.Parse(value);
        }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, mValue);
        }
    }
    [AttributeUsage(AttributeTargets.Property)]
    public class Enabled : ValueAttribute
    {
        public Enabled() : base(false) { }
        public override void Executing(IConnectinContext cc, object data, PropertyMapper pm, string table)
        {
            pm.Handler.Set(data, true);
        }
    }