基于firebase中多个where子句的查询 [英] Query based on multiple where clauses in firebase
问题描述
{
movies：{
movie1：{
genre：comedy，
name ：
lead：Jack Nicholson
}，
movie2：{
genre：Horror，
name：The Shining，
lead：Jack Nicholson
}，
movie3：{
流派：喜剧，
name：The Mask，
lead：Jim Carrey
}
}
}
我是Firebase新手。如何从上面的数据检索结果，其中genre ='喜剧'AND lead ='Jack Nicholson'？
我有什么选择？提前致谢。
// !!!这将无法正常工作！
ref
.orderBy（'genre'）
.startAt（'comedy'）。endAt（'comedy'）
.orderBy（'lead'）//这条线将升起一个错误！
.startAt（'Jack Nicholson'）。endAt（'Jack Nicholson'）
.on（'value'，function（snapshot）{
console.log（snapshot.val（）） ;
}）;
但是Firebase的@RobDiMarco在评论中说：
多个
orderBy（）调用会抛出错误
所以我的代码无法正常工作。
我知道有三种方法可行。
1。在服务器上过滤大部分内容，在客户端执行其他操作。
你可以执行一个 orderBy .startAt（）./ endAt（），在客户端上拉下剩下的数据并用JavaScript代码过滤。
$ b
ref
.orderBy（'genre'）
.equalTo '喜剧'）
.on（'child_added'，function（snapshot）{
var movie = snapshot.val（）;
if（movie.lead =='Jack Nicholson'）{
console.log（movie）;
}
}）;
2。添加一个属性，该属性结合了您要过滤的值
如果这样做不够好，您应该考虑修改/扩展数据以允许您的用例。信息中信息内读范范范中内的数范范信息范范中范范内信息
movie1：{
genre：comedy，
name
lead：Jack Nicholson，
genre_lead：comedy_Jack Nicholson
}，...
您本质上是以这种方式构建您自己的多列索引，并可以使用以下查询：
ref
.orderBy（'genre_lead'）
.equalTo（'comedy_Jack Nicholson'）
.on（'child_added'，function快照）{
var movie = snapshot.val（）;
console.log（movie）;
}）;
David East写了一个
你甚至可以做相对/范围查询，比如说你希望允许按类别和年份查询电影。你可以使用这个数据结构：
$ $ p $movie1：{
genre：comedy，$
lead：Jack Nicholson，
genre_year：comedy_1997
}，...
然后查询90年代的喜剧片：
< pre $ ref
.orderBy（'genre_year'）
.startAt（'comedy_1990'）
.endAt（'comedy_2000'）
。 on（'child_added'，function（snapshot）{
var movie = snapshot.val（）;
console.log（movie）;
}）;
如果您需要过滤一年以上，请确保将其他日期部分添加到降序，例如 comedy_1997-12-25。通过这种方式，Firebase在字符串值上的字典顺序将与时间顺序相同。
这个属性中的值的组合可以使用两个以上的值，但是您只能对组合属性中的最后一个值进行范围过滤。
一个非常特殊的变体是由 GeoFire库为Firebase 。这个图书馆将一个地点的经度和纬度组合成一个所谓的 Geohash ，然后就可以用于在Firebase上进行实时范围查询。
3。以编程方式创建自定义索引另一种方法是在添加新的Query API之前完成所有工作：在不同节点中创建索引：
$ $ p $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $
by_lead
Jack Nicholson
movie1
Jim Carrey
movie3
恐怖
by_lead
Jack Nicholson
movie2
方法。例如，此答案突出显示了另一种树状自定义索引： https://stackoverflow.com/a/34105063
{
"movies": {
"movie1": {
"genre": "comedy",
"name": "As good as it gets",
"lead": "Jack Nicholson"
},
"movie2": {
"genre": "Horror",
"name": "The Shining",
"lead": "Jack Nicholson"
},
"movie3": {
"genre": "comedy",
"name": "The Mask",
"lead": "Jim Carrey"
}
}
}
I am Firebase newbie. How can I retrieve a result from the data above where genre = 'comedy' AND lead = 'Jack Nicholson' ?
What options do I have? Thanks in advance.
Using Firebase's new Query API, you might be tempted to try this:
// !!! THIS WILL NOT WORK !!!
ref
.orderBy('genre')
.startAt('comedy').endAt('comedy')
.orderBy('lead') // !!! THIS LINE WILL RAISE AN ERROR !!!
.startAt('Jack Nicholson').endAt('Jack Nicholson')
.on('value', function(snapshot) {
console.log(snapshot.val());
});
But as @RobDiMarco from Firebase says in the comments:
multiple
orderBy()calls will throw an error
So my code above will not work.
I know of three approaches that will work.
1. filter most on the server, do the rest on the client
What you can do is execute one orderBy().startAt()./endAt() on the server, pull down the remaining data and filter that in JavaScript code on your client.
ref
.orderBy('genre')
.equalTo('comedy')
.on('child_added', function(snapshot) {
var movie = snapshot.val();
if (movie.lead == 'Jack Nicholson') {
console.log(movie);
}
});
2. add a property that combines the values that you want to filter on
If that isn't good enough, you should consider modifying/expanding your data to allow your use-case. For example: you could stuff genre+lead into a single property that you just use for this filter.
"movie1": {
"genre": "comedy",
"name": "As good as it gets",
"lead": "Jack Nicholson",
"genre_lead": "comedy_Jack Nicholson"
},...
You're essentially building your own multi-column index that way and can query it with:
ref
.orderBy('genre_lead')
.equalTo('comedy_Jack Nicholson')
.on('child_added', function(snapshot) {
var movie = snapshot.val();
console.log(movie);
});
David East has written a library called QueryBase that helps with generating such properties.
You could even do relative/range queries, let's say that you want to allow querying movies by category and year. You'd use this data structure:
"movie1": {
"genre": "comedy",
"name": "As good as it gets",
"lead": "Jack Nicholson",
"genre_year": "comedy_1997"
},...
And then query for comedies of the 90s with:
ref
.orderBy('genre_year')
.startAt('comedy_1990')
.endAt('comedy_2000')
.on('child_added', function(snapshot) {
var movie = snapshot.val();
console.log(movie);
});
If you need to filter on more than just the year, make sure to add the other date parts in descending order, e.g. "comedy_1997-12-25". This way the lexicographical ordering that Firebase does on string values will be the same as the chronological ordering.
This combining of values in a property can work with more than two values, but you can only do a range filter on the last value in the composite property.
A very special variant of this is implemented by the GeoFire library for Firebase. This library combines the latitude and longitude of a location into a so-called Geohash, which can then be used to do realtime range queries on Firebase.
3. create a custom index programmatically
Yet another alternative is to do what we've all done before this new Query API was added: create an index in a different node:
"movies"
// the same structure you have today
"by_genre"
"comedy"
"by_lead"
"Jack Nicholson"
"movie1"
"Jim Carrey"
"movie3"
"Horror"
"by_lead"
"Jack Nicholson"
"movie2"
There are probably more approaches. For example, this answer highlights an alternative tree-shaped custom index: https://stackoverflow.com/a/34105063
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