/// <summary>
/// 生成表达式
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="parameter">参数表达式</param>
/// <param name="member">成员表达式</param>
/// <param name="value">属性值</param>
/// <param name="operator">操作符</param>
/// <exception cref="ArgumentNullException"></exception>
/// <exception cref="NotSupportedException"></exception>
/// <returns></returns>
public static Expression <Func <T, bool> > Create <T>(ParameterExpression parameter, MemberExpression member, object value, SQLOperator @operator)
{
if (parameter is null)
{
throw new ArgumentNullException(nameof(parameter));
}
if (member is null)
{
throw new ArgumentNullException(nameof(member));
}
switch (@operator)
{
case SQLOperator.Contains:
case SQLOperator.EndWith:
case SQLOperator.StartsWith:
if (value != null && value.GetType() != typeof(string))
{
throw new NotSupportedException($"{nameof(SQLOperator)}.{@operator}只适用于string类型");
}
var method = typeof(string).GetMethod(@operator.ToString(), new[] { typeof(string) });
var body = Expression.Call(member, method, ConstantExpression(value, typeof(string)));
return(Expression.Lambda(body, parameter) as Expression <Func <T, bool> >);
default:
var valueExp = ConstantExpression(value, member.Type);
var binaryBody = Expression.MakeBinary((ExpressionType)@operator, member, valueExp);
return(Expression.Lambda(binaryBody, parameter) as Expression <Func <T, bool> >);
}
}
