private Expression ParseValue(QueryCondition condition)
{
Expression value = Expression.Constant(condition.Value);
return(value);
}
private Expression ParseMethod(Expression key, Expression value, QueryCondition condition)
{
switch (condition.Operator)
{
case QueryOperator.CONTAINS:
return(Expression.Call(key, typeof(string).GetMethod("Contains"), value));
case QueryOperator.EQUAL:
return(Expression.Equal(key, Expression.Convert(value, key.Type))); //黎又铭 update 2016.5.27 修复类型 Nullable
case QueryOperator.GERATER:
return(Expression.GreaterThan(key, Expression.Convert(value, key.Type)));
case QueryOperator.GREATEROREQUAL:
return(Expression.GreaterThanOrEqual(key, Expression.Convert(value, key.Type)));
case QueryOperator.LESS:
return(Expression.LessThan(key, Expression.Convert(value, key.Type)));
case QueryOperator.LESSOREQUAL:
return(Expression.LessThanOrEqual(key, Expression.Convert(value, key.Type)));
case QueryOperator.NotEqual:
return(Expression.NotEqual(key, Expression.Convert(value, key.Type)));
case QueryOperator.IN:
ConstantExpression constand = value as ConstantExpression;
string[] names = constand.Value.ToString().Split(',');
var equals = new List <BinaryExpression>() // 创建一个永远不可能为true的表达式,如果equals count = 0, Aggregate将会报错
{
Expression.MakeBinary(ExpressionType.Equal, Expression.Constant(false), Expression.Constant(true))
};
foreach (var item in names)
{
int result;
if (int.TryParse(item, out result))
{
var t = Expression.Equal(key, Expression.Convert(Expression.Constant(Convert.ToInt32(item)), key.Type));
equals.Add(t);
}
else if (item.ToLower() == "null") // nullable<>, class 等类型才可能有NULL,不要使用在值类型的对象上加入null的值
{
equals.Add(Expression.Equal(key, Expression.Constant(null)));
}
}
//Expression body = Expression.Constant(false); // or操作必须用flase 否则可能有意外成功
//if (equals.Any()) { // 如果equals.count=0,Aggregate会报错
// body = equals.Aggregate<Expression>((acc,condation) => Expression.OrElse(acc,condation));
// // 手写Aggregate()方法的实现
// //Expression body2 = Expression.Constant(false);
// //foreach (var item in equals) {
// // body2 = Expression.OrElse(body2, item);
// //}
// //body = body2;
//}
var body = equals.Aggregate <Expression>((acc, condation) => Expression.OrElse(acc, condation));
return(body);
default:
throw new NotImplementedException(); //Operator IN is difficult to implenment. Wait a sec.....
}
}