使用filter和getNearest命令进行rethinkdb [英] rethinkdb with filter and getNearest commands

问题描述

如何执行关于其他命令(例如过滤器命令)结果的getNearest查询?

How can execute getNearest query about the result of other command, for example a filter command?

var point = r.point(-122.422876,37.777128);  
r.db('test').table('users').
   filter({tags : 'tag'}).
   getNearest(point, {index: 'geodata', maxResults: 30, unit :'km'})

我有一个用户"表:

 [ 
   {id: 1, tags : ['music', 'cups'], geodata: r.point()} 
   {id: 2, tags: ['music', 'play'], geodata: r.point()} 
 ] 

首先，我想按标签"字段进行过滤，然后返回最接近的值.

First I want to filter by 'tags' field and then return the nearest.

我指定的查询不正确，返回以下错误:" RqlRuntimeError:预期类型为TABLE但找到了SELECTION "

The query that I have specified is incorrect, return the follow error: "RqlRuntimeError: Expected type TABLE but found SELECTION"

推荐答案

查询引发错误的原因是

The reason why your query throws an error is because .getNearest only works with tables. That's what the documentation says.

选项1

您可以通过反转命令的顺序来解决问题:

You can solve your problem by just inverting the order of of commands:

var point = r.point(-122.422876,37.777128);  
r.db('test')
 .table('users')
 .getNearest(point, {index: 'geodata', maxResults: 30, unit :'km'})
 .filter({tags : 'tag'})

之所以可行，是因为.getNearest返回一个数组，而.filter可以在一个数组上工作.

This works because .getNearest returns an array and .filter can work on an array.

var point = r.point(-122.422876,37.777128);  
r.db('test')
 .table('users')
 .getNearest(point, {index: 'geodata', unit :'km'})
 .filter({tags : 'tag'})
 .limit(30)

此方法的问题在于，为了保证所有可能的结果都存在，您不能将maxResults选项传递给getNearest，这意味着将查询并过滤每一行.

The problem this approach is that, in order to guarantee that all possible results are there, you can't pass a maxResults option to getNearest, which means every single row will be queried and then filtered.

这种情况最适合大多数物品通过过滤器的情况.

This scenario works best for when most items will pass through the filter.

根据您的数据，还可以编写一个递增地递增maxResults的函数，直到获得所需的所有结果为止，但这可能很复杂而且不太优雅.

Depending on your data, it's also possible to write a function that increases maxResults incrementally until it gets all the results it needs, but this might be complex and not very elegant.

选项2

如果过滤器要过滤掉大部分结果，则可以使用 getAll (创建tags索引)，并先getAll过滤结果，然后根据距离对结果进行排序:

If the filter is going to filter out most of the results, then you can filter the results using getAll (creating a tags index) and have getAll filter the results first and then order the results based on distance:

var point = r.point(-122.422876,37.777128);
r.table('users')
 .getAll('tag', {index: 'tags'})
 .orderBy(r.row('geodata')
 .distance(point))
 .limit(30)

数据类型

使用 .typeOf 方法.

You can always get the type of a anything at any point by using the .typeOf method.

示例:

r.db('test')
 .table('users').typeOf() // "TABLE"

r.db('test')
 .table('users')
 .filter({tags : 'tag'}).typeOf() // "STREAM"

如果您想了解有关ReQL数据类型的更多信息，可以查看此博客文章我写的文章解释了ReQL数据类型及其不同之处.

If you want to know more about ReQL data types, you can check out this blog post I wrote which explains ReQL data types and how they are different.

这篇关于使用filter和getNearest命令进行rethinkdb的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！