ORMLite - 退货项目瓦特/最大ID（或价值） [英] ORMLite - return item w/ maximum ID (or value)

问题描述

我使用ORMLite瓦特/ Android系统。我想抓住对象的ID值w /最高值ID。

I'm using ORMLite w/ Android. I want to grab the ID value of the object w/ the highest-valued ID.

我也想推广这要求单个对象W /最大/最小值的任意字段。什么是最好的做法这样做呢？

I'd also like to generalize this to requesting a single object w/ max/min value for any arbitrary field. What is the best practice for doing this?

我知道我可以执行原始查询，但那里跳了出来，在任何人的任何其他方式？我想象类似iOS上执行的的coredata FetchRequests时predicates东西。

I realize I could execute a raw query, but is there any other way that jumps out at anyone? I'm imagining something similar to Predicates when executing FetchRequests in CoreData on iOS.

推荐答案

您的答案看起来不错@Ben但我想我会放弃给后人一些额外的信息：

Your answer looks good @Ben but I thought I'd give some extra info for posterity:

1. 您可以使用 queryForFirst 如果你知道你的限制（1）将返回一个结果

1. You could use a queryForFirst if you know your limit(1) will return a single result.

qBuilder.orderby("my_field_column_name", false);
qBuilder.limit(1L);
MyEntity maxEntity = myEntityDao.queryForFirst(qBuilder.prepare());

一个原始查询也将工作。它涉及多个对象和检查，但将是，如果表的大小是大便宜，因为你不需要做排序。

A raw query would also work. It involves more objects and checking but will be cheaper if the table size is large since you don't need to do the ordering.

qBuilder.selectRaw("MAX(my_field_column_name)");
GenericRawResults<String[]> results =
    myEntityDao.queryRaw(qBuilder.prepareStatementString());
String[] result = results.getResults().next();
int max = Integer.parseInt(result[0]);

显然，如果你的列是一个不同的类型，那么你会得到一个不同的对象出了结果[0] ，你将不得不转换成根据相应的类型对象

Obviously, if your column was a different type then you would get a different object out of result[0] that you would have to convert into the appropriate type depending on the object.

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