客观化查询字段不为空的所有记录的有效方法 [英] Efficient way to query all records where a field is not null in objectify

问题描述

我想有效地查询索引字段以检索索引字段不为空（存在于索引中）的所有记录。要查询的字段包含 Ref< T> 到另一个实体，以防相关。

什么我能做的就是一个不等式搜索，比如 .filter / .filterKey（fieldname> =，a），其中a是我想要的最小的ASCII抓住。

但是这是否有效？或者我可以以某种方式进行平等搜索，它会返回索引中存在的所有记录？

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这就是我的数据的样子：我想过滤overlay列中有关键字的所有记录，并省略那些未设置字段的记录。如果可能的话，我想使用平等过滤器，所以我不需要组合索引（因为我在同一时间在其他字段上进行过滤）。

img src =https://i.stack.imgur.com/lTnEE.pngalt =资料快照>

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我可以用它来测试！= null

  .filter（user>，\\\�）; 
  

，并且测试 == null

  .filter（user<，\\\�）; 
  

我想这不是它应该完成的方式。有没有办法解决这个问题，使用相等而不是不平等？

解决方案

如果您想要查询具有null值为一个索引字段：

  ofy（）。load（）.type（Thing.class）.filter（fieldname！ =，null）
  

然而，这与平等过滤器不同。在封面之下，GAE将！=视为一对过滤器（>和<），这带来了不平等过滤器的限制。

如果您需要一个等式过滤not null，在您的实体中创建一个合成索引字段，该字段使用@OnSave方法填充。您可以对'真'值使用部分索引来限制索引这些额外数据的成本（即 @Index（IfTrue.class））

I want to query an indexed field efficiently to retrieve all records where the indexed field is not null (present in the index). The field to be queried contains a Ref<T> to another entity, in case this is relevant.

What I could do is an inequality search, like .filter/.filterKey("fieldname >=", "a"), where a is the smallest ASCII that I want to grab.

But is this efficient? Or can I do an equality search somehow, which returns all records that are present in the index?

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This is how my data looks like: I want to filter all records where the "overlay" column has a key, and omit those where the field is not set. I would like to use an equality filter if possible, so I don't need a composite index (as I am filtering on other fields at the same time).

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I can use this to test for != null

.filter("user >", "\uFFFD");

and this to test for == null

.filter("user <", "\uFFFD");

I guess that's not the way it should be done. Is there a way to solve this problem using equality instead of inequality?

解决方案

If you want to query for entities which have a null value for an indexed field:

ofy().load().type(Thing.class).filter("fieldname !=", null)

However, this is not the same thing as an equality filter. Under the covers, GAE treats != as a pair of filters (> and <) and this brings with it the limitations of inequality filters.

If you need an equality filter on "not null", create a synthetic indexed field in your entity which is populated using an @OnSave method. You can use a partial index on the 'true' value to limit the cost of indexing this extra data (ie, @Index(IfTrue.class))

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