c# - 根据方法参数构建 IQueryable

Question

我有一个类似于下面的 API 方法。

是否可以附加 IQueryable 以便最终查询具有执行 where 语句的项目列表，或者我应该使用 SqlQuery 属性并构建原始 SQL 字符串。

    public IEnumerable<Message> GetMessagesFromApi(DateTime? dateFrom = null, DateTime? dateTo = null, int flag = -1, int messageType = 1, bool media =false)
    {
        if (dateFrom == null)
            dateFrom = DateTime.MinValue;

        if (dateTo == null)
            dateTo = DateTime.MaxValue;

        IQueryable<Message> query = null;


        query = db.Messages.Where(x => x.Created >= dateFrom && x.Created <= dateTo);


        if (flag >= 0)
        {
            //Append the where statement on dates to now include Flag
            query = query.Where(x => x.Flag == flag);
        }

       //Here it should execute against Where date >= and date <= and flag = 1
    }

Answer 1

Is it possible to append the IQueryable so the final query has a list of items to execute a where statement.

是的。您的代码应该可以正常工作。如果你想构建一个 IEnumerable<Message>，你只需要执行这个对于结果。

//Here it should execute against Where date >= and date <= and flag = 1
return query.ToList();

请注意，您可以使用 AsEnumerable()甚至只是返回 query直接(因为 IQueryable<T> 实现了 IEnumerable<T> )，但如果用户多次枚举您的结果，这将导致问题，因为每次枚举都会命中数据库。

我个人会这样写:

public IEnumerable<Message> GetMessagesFromApi(DateTime? dateFrom = null, DateTime? dateTo = null, int flag = -1, int messageType = 1, bool media =false)
{
    IQueryable<Message> query = db.Messages;

    if(dateFrom.HasValue)
        query = query.Where(x => x.Created >= dateFrom);
    if(dateTo.HasValue)
        query = query.Where(x => x.Created <= dateTo);
    if(flag >= 0)
        query = query.Where(x => x.Flag == flag);
    // others as needed, such as media...

    return query.ToList();
}