Linq If Statement

Question

我如何在linq中向实体写这样的东西

sb.Append(" WHERE question.question_isdeleted = 0");
    if (catid != 0)
        sb.AppendFormat(" AND (CatID IN ({0}))", catsSTR);
    if(!string.IsNullOrEmpty(AuthorID))
        sb.Append(" AND (question_ownerid = @id)");

我想我只需要在linq中为实体写一个if条件的语法

Answer 1

我会在这里使用点符号:

var query = questions.Where(q => !q.IsDeleted);

if (catId != 0)
{
    query = query.Where(q => cats.Contains(q.CatID));
}
if (authorId != 0)
{
    query = query.Where(q => q.OwnerId == authorId);
}

您可以编写自己的扩展方法来更简单地执行此操作:

public static IQueryable<T> OptionalWhere<T>(
    this IQueryable<T> source,
    bool condition, 
    Expression<Func<T,bool>> predicate)
{
    return condition ? source.Where(predicate) : source;
}

然后你可以写:

var query = questions.Where(q => !q.IsDeleted);
                     .OptionalWhere(catId != 0, q => cats.Contains(q.CatID))
                     .OptionalWhere(authorId != 0, q => q.OwnerId == authorId);