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{
"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 a Firebase newbie. How can I retrieve a result from the data above where genre = 'comedy' AND lead = 'Jack Nicholson'?
What options do I have?
Using Firebase's 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
If none of these options work for you, but you still want to store your data in Firebase, you can also consider using its Cloud Firestore database.
Cloud Firestore can handle multiple equality filters in a single query, but only one range filter. Under the hood it essentially uses the same query model, but it's like it auto-generates the composite properties for you. See Firestore's documentation on compound queries.
I've written a personal library that allows you to order by multiple values, with all the ordering done on the server.
Meet Querybase!
Querybase takes in a Firebase Database Reference and an array of fields you wish to index on. When you create new records it will automatically handle the generation of keys that allow for multiple querying. The caveat is that it only supports straight equivalence (no less than or greater than).
const databaseRef = firebase.database().ref().child('people');
const querybaseRef = querybase.ref(databaseRef, ['name', 'age', 'location']);
// Automatically handles composite keys
querybaseRef.push({
name: 'David',
age: 27,
location: 'SF'
});
// Find records by multiple fields
// returns a Firebase Database ref
const queriedDbRef = querybaseRef
.where({
name: 'David',
age: 27
});
// Listen for realtime updates
queriedDbRef.on('value', snap => console.log(snap));
var ref = new Firebase('https://your.firebaseio.com/');
Query query = ref.orderByChild('genre').equalTo('comedy');
query.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot movieSnapshot : dataSnapshot.getChildren()) {
Movie movie = dataSnapshot.getValue(Movie.class);
if (movie.getLead().equals('Jack Nicholson')) {
console.log(movieSnapshot.getKey());
}
}
}
#Override
public void onCancelled(FirebaseError firebaseError) {
}
});
Frank's answer is good but Firestore introduced array-contains recently that makes it easier to do AND queries.
You can create a filters field to add you filters. You can add as many values as you need. For example to filter by comedy and Jack Nicholson you can add the value comedy_Jack Nicholson but if you also you want to by comedy and 2014 you can add the value comedy_2014 without creating more fields.
{
"movies": {
"movie1": {
"genre": "comedy",
"name": "As good as it gets",
"lead": "Jack Nicholson",
"year": 2014,
"filters": [
"comedy_Jack Nicholson",
"comedy_2014"
]
}
}
}
For Cloud Firestore
https://firebase.google.com/docs/firestore/query-data/queries#compound_queries
Compound queries
You can chain multiple equality operators (== or array-contains) methods to create more specific queries (logical AND). However, you must create a composite index to combine equality operators with the inequality operators, <, <=, >, and !=.
citiesRef.where('state', '==', 'CO').where('name', '==', 'Denver');
citiesRef.where('state', '==', 'CA').where('population', '<', 1000000);
You can perform range (<, <=, >, >=) or not equals (!=) comparisons only on a single field, and you can include at most one array-contains or array-contains-any clause in a compound query:
Firebase doesn't allow querying with multiple conditions.
However, I did find a way around for this:
We need to download the initial filtered data from the database and store it in an array list.
Query query = databaseReference.orderByChild("genre").equalTo("comedy");
databaseReference.addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
ArrayList<Movie> movies = new ArrayList<>();
for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
String lead = dataSnapshot1.child("lead").getValue(String.class);
String genre = dataSnapshot1.child("genre").getValue(String.class);
movie = new Movie(lead, genre);
movies.add(movie);
}
filterResults(movies, "Jack Nicholson");
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
}
});
Once we obtain the initial filtered data from the database, we need to do further filter in our backend.
public void filterResults(final List<Movie> list, final String genre) {
List<Movie> movies = new ArrayList<>();
movies = list.stream().filter(o -> o.getLead().equals(genre)).collect(Collectors.toList());
System.out.println(movies);
employees.forEach(movie -> System.out.println(movie.getFirstName()));
}
The data from firebase realtime database is as _InternalLinkedHashMap<dynamic, dynamic>.
You can also just convert this it to your map and query very easily.
For example, I have a chat app and I use realtime database to store the uid of the user and the bool value whether the user is online or not. As the picture below.
Now, I have a class RealtimeDatabase and a static method getAllUsersOnineStatus().
static getOnilineUsersUID() {
var dbRef = FirebaseDatabase.instance;
DatabaseReference reference = dbRef.reference().child("Online");
reference.once().then((value) {
Map<String, bool> map = Map<String, bool>.from(value.value);
List users = [];
map.forEach((key, value) {
if (value) {
users.add(key);
}
});
print(users);
});
}
It will print [NOraDTGaQSZbIEszidCujw1AEym2]
I am new to flutter If you know more please update the answer.
ref.orderByChild("lead").startAt("Jack Nicholson").endAt("Jack Nicholson").listner....
This will work.
I want to extract value from dynamic JSON.
This generation is different every time when is executed.
I need to get ex: XLIfccMNLv1asVam3QuatowCmrp8IYuE0FUDMYncegs=
which is generated in the different location in the Json file, with different value
I tried with.
$.payload[?(#.eventType == 'AAA')].entityId
which is working fine.
But, i want more stronger query.
Is it possible to use && statement with the query something like:
$.payload[?(#.eventType == 'AAA')&&(#.outgoingCurrency== 'EUR')].entityId
My payload:
{
"payload":[
{
"entityId":"qvr_IlDhTdzldeccxguNR84sE0N78DUfNGzwH-3pY7Y=",
"accountHolderId":"dvwxpTxVHdo2n1d5ytO6WyhnI2nuaEuzsh47agPpSFU=",
"processorType":"DUMMY",
"eventType":"AAA",
"outgoingCurrency":"USD",
"holdPeriodInHours":11,
"disabled":false
},
{
"entityId":"XLIfccMNLv1asVam3QuatowCmrp8IYuE0FUDMYncegs=",
"accountHolderId":"Xoo8uAM90qRT7kceDUJBIIqafUuUdH2fH_Ia2z1TY5w=",
"processorType":"DUMMY",
"eventType":"BBB",
"outgoingCurrency":"EUR",
"holdPeriodInHours":10,
"disabled":false
},
{
"entityId":"yBoHvYkyszaQpaFe1zvqCY416_vYiq7iivA9bWJhiTg=",
"processorType":"BMO_CPR",
"eventType":"AAA",
"disabled":false
}
]
}
You need to use the operation && inside the expression:
$.payload[?(#.outgoingCurrency== 'EUR' && #.eventType == 'AAA')].entityId.
For more details see: https://goessner.net/articles/JsonPath/
Im trying to work out how to append a zero to a specific JSON decoded array value for multiple records stored in a MySQL table according to some conditions.
for example, for table 'menu', column 'params'(text) have records containing JSON decoded arrays of this format:
{"categories":["190"],"singleCatOrdering":"","menu-anchor_title":""}
and column 'id' has a numeric value of 90.
my goal is to add a zero to 'categories' value in menu.params whenever (for example) menu.id is under 100.
for this records the result being
{"categories":["1900"],"singleCatOrdering":"","menu-anchor_title":""}
so im looking for a SQL Query that will search and find the occurrences of "categories": ["999"] in the Database and update the record by adding a zero to the end of the value.
this answer is partially helpful by offering to use mysql-udf-regexp but its referring to REPLACE a value and not UPDATE it.
perhaps the REGEXP_REPLACE? function will do the trick. i have never used this library and am not familiar with it, perhaps there is an easier way to achieve what i need ?
Thanks
If I understand your question correctly, you want code that does something like this:
var data = {
"menu": {
"id": 90,
"params": {
"categories": ["190"],
"singleCatOrdering": "",
"menu-anchor_title": ""
}
}
};
var keys = Object.keys(data);
var columns;
for (var ii = 0, key; key = keys[ii]; ii++) {
value = data[key];
if (value.id < 100) {
value.params.categories[0] += "0";
alert(value.params.categories[0]);
}
}
jsFiddle
However, I am not using a regular expression at all. Perhaps if you reword the question, the necessity of a regex will become clearer.
I presume a simple question. I have the following data.
I want to search for all rows where the ID is > 2 but < 8 and the Price is > 30
I have used various versions of: startkey=["2", null] or even something like startkey=["2", "30"] just for testing.
It only ever seems to run both conditions on the first row. So if I do: startkey=["2", "30"] then I get back:
{"id":"3","key":["3","30"],"value":null},
{"id":"4","key":["4","30"],"value":null},
{"id":"5","key":["5","20"],"value":null},
{"id":"6","key":["6","60"],"value":null},
{"id":"8","key":["8","60"],"value":null}
Why is row 5 there?
I am starting to get the view that I need to handle this in the code (.net) and make multiple calls somehow... I can't seem to find anything on this that works....
Note: I have tried doing say a loop with for (i = 0; i < doc.ID.length; i++) and then using doc.ID[i] but it never returns anything....
Currently I just have
function (doc, meta) {
emit([doc.ID, doc.Price ],null);
}
Essentially I want to have a search where there are 5 input keys that a user has. So do I need to make 5 calls and then keep taking data from the previous output as the source for the next???
Other references I have looked at include: the manual
Thanks in advance,
Kindest Regards
Robin
This is a common misconception, with a compound array index key, it's still treated as a string, therefore the index key [2,10] is actually "[2,10]", and the index key [5,20], is actually "[5,20]".
So the reason that startkey=["2", "30"]shows the {"id":"5","key":["5","20"],"value":null}, row is because as a string it is > startkey.
Likewise, the Query startkey=[2,10]&endkey=[5,10] returns
{"total_rows":7,"rows":[
{"id":"2","key":[2,20],"value":null},
{"id":"3","key":[3,30],"value":null},
{"id":"4","key":[4,30],"value":null}
]
}
because startkey="[2,10]" < "[2,20]" && "[4,30]" < "[5,10]"=endkey, but "[5,20]" is not within that string Range.
Range Queries with startkey and endkey
startkey => endkey is a Range query using strcmp(), the group and group level is based on the string, where the comma is separating string tokens.
A Good Reference Link (since Couchbase Views work much like Apache CouchDB Views (inspired by them))
http://wiki.apache.org/couchdb/View_collation#Collation_Specification
Spatial View/Query
To achieve the result you are trying for, you could also write a Spatial View to have multi-dimensional Queries, numeric only. While you might not initially think of it
function (doc, meta) {
emit({
type: "Point",
coordinates: [doc.ID, doc.Price]
}, meta.id);
}
The Query would be a Bounding Box Query:
&bbox=2,0,8,30
{"total_rows":0,"rows":[
{"id":"2","bbox":[2,20,2,20],"geometry":{"type":"Point","coordinates":[2,20]},"value":"2"},
{"id":"3","bbox":[3,30,3,30],"geometry":{"type":"Point","coordinates":[3,30]},"value":"3"},
{"id":"4","bbox":[4,30,4,30],"geometry":{"type":"Point","coordinates":[4,30]},"value":"4"},
{"id":"5","bbox":[5,20,5,20],"geometry":{"type":"Point","coordinates":[5,20]},"value":"5"}
]
}
Another Query:
&bbox=2,30,8,30
{"total_rows":0,"rows":[
{"id":"3","bbox":[3,30,3,30],"geometry":{"type":"Point","coordinates":[3,30]},"value":"3"},
{"id":"4","bbox":[4,30,4,30],"geometry":{"type":"Point","coordinates":[4,30]},"value":"4"}
]
}
What would be the best way to filter records from a view based on tags in couchbase? I mean I understand that I can extract tags from the documents and use them as the keys using the map functionality in the view. But is there a way to select records from the view based on whether the record's key (which can be multiple values) contains a tag?
Example: I have a transaction that has the following tags (tag 1, tag2, tag3, tag4) and each view record (from the emit function) looks like this
emit ([tag1,tag2,tag3,tag4], null)
What I want to get is all the records that have tag2.
Thanks for any help.
Two suggestions... If the only purpose of the view is to find records with a particular tag, you could simply emit a view row for each tag.
function (doc) {
if (doc.tags) {
for(var idx in doc.tags) {
emit(doc.tags[idx], null);
}
}
}
This map function would give you rows as follows:
{"total_rows":13,"rows":[
{"id":"foo_doc_1","key":"a","value":null},
{"id":"foo_doc_3","key":"a","value":null},
{"id":"foo_doc_1","key":"b","value":null},
{"id":"foo_doc_2","key":"b","value":null},
{"id":"foo_doc_3","key":"b","value":null},
{"id":"foo_doc_1","key":"c","value":null},
{"id":"foo_doc_2","key":"c","value":null},
{"id":"foo_doc_1","key":"d","value":null},
{"id":"foo_doc_4","key":"d","value":null},
{"id":"foo_doc_4","key":"e","value":null}
]
}
When you query by key (e.g., key="a") you'll get the results for that key. If however, your concern is "give me all documents where the second tag is 'xyz'" then you could emit the index as well.
function (doc) {
if (doc.tags) {
for(var idx in doc.tags) {
emit([parseInt(idx), doc.tags[idx]], null);
}
}
}
In this example, the rows would like like:
{"total_rows":13,"rows":[
{"id":"foo_doc_1","key":[0,"a"],"value":null},
{"id":"foo_doc_3","key":[0,"a"],"value":null},
{"id":"foo_doc_2","key":[0,"b"],"value":null},
{"id":"foo_doc_4","key":[0,"d"],"value":null},
{"id":"foo_doc_1","key":[1,"b"],"value":null},
{"id":"foo_doc_3","key":[1,"b"],"value":null},
{"id":"foo_doc_2","key":[1,"c"],"value":null},
{"id":"foo_doc_4","key":[1,"e"],"value":null},
{"id":"foo_doc_1","key":[2,"c"],"value":null},
{"id":"foo_doc_4","key":[2,"f"],"value":null}
]
}
You would then query with an array key to get a key at a particular position (e.g., key=[1, "b"]).