/// <summary>
/// 根据设定的字段，生成查询重复数据的Lambda，最终返回类似 x=>x.property == val的lambda
/// </summary>
/// <param name="Entity">要验证字段的实体类</param>
/// <param name="para">ParameterExpression</param>
/// <returns></returns>
public virtual Expression GetExpression(T Entity, ParameterExpression para)
{
var propName = PropertyHelper.GetPropertyName(_directFieldExp);
var prop = PropertyHelper.GetPropertyInfo(_directFieldExp);
var func = _directFieldExp.Compile();
var val = func.Invoke(Entity);
////如果字段值为null则跳过，因为一般情况下null值不会被认为重复
//if (val == null)
//{
// return res;
//}
//如果字段值是空字符串，则跳过
if (val is string && val.ToString() == string.Empty)
{
var requiredAttrs = prop.GetCustomAttributes(typeof(RequiredAttribute), false).ToList();
if (requiredAttrs == null || requiredAttrs.Count == 0)
{
return(null);
}
else
{
var requiredAtt = requiredAttrs[0] as RequiredAttribute;
if (requiredAtt.AllowEmptyStrings == true)
{
return(null);
}
}
}
//生成一个表达式，类似于 x=>x.field == val
var splits = propName.Split('.');
var idproperty = typeof(T).GetProperties().Where(x => x.Name == splits[0]).FirstOrDefault();
Expression left = Expression.Property(para, idproperty);
for (int i = 1; i < splits.Length; i++)
{
var tempproperty = typeof(T).GetProperties().Where(x => x.Name == splits[i]).FirstOrDefault();
left = Expression.Property(left, tempproperty);
}
if (val != null && left.Type.IsGeneric(typeof(Nullable <>)))
{
left = Expression.Property(left, "Value");
}
if (left.Type == typeof(string))
{
left = Expression.Call(left, typeof(String).GetMethod("Trim", Type.EmptyTypes));
}
if (val is string)
{
val = val.ToString().Trim();
}
var right = Expression.Constant(val);
var equal = Expression.Equal(left, right);
return(equal);
}
public virtual List <PropertyInfo> GetProperties()
{
List <PropertyInfo> rv = new List <PropertyInfo>
{
PropertyHelper.GetPropertyInfo(_directFieldExp)
};
return(rv);
}
