Given the data structure below in firebase, i want to run a query to retrieve the blog 'efg'. I don't know the user id at this point.
{Users :
"1234567": {
name: 'Bob',
blogs: {
'abc':{..},
'zyx':{..}
}
},
"7654321": {
name: 'Frank',
blogs: {
'efg':{..},
'hij':{..}
}
}
}
The Firebase API only allows you to filter children one level deep (or with a known path) with its orderByChild and equalTo methods.
So without modifying/expanding your current data structure that just leaves the option to retrieve all data and filter it client-side:
var ref = firebase.database().ref('Users');
ref.once('value', function(snapshot) {
snapshot.forEach(function(userSnapshot) {
var blogs = userSnapshot.val().blogs;
var daBlog = blogs['efg'];
});
});
This is of course highly inefficient and won't scale when you have a non-trivial number of users/blogs.
So the common solution to that is to a so-called index to your tree that maps the key that you are looking for to the path where it resides:
{Blogs:
"abc": "1234567",
"zyx": "1234567",
"efg": "7654321",
"hij": "7654321"
}
Then you can quickly access the blog using:
var ref = firebase.database().ref();
ref.child('Blogs/efg').once('value', function(snapshot) {
var user = snapshot.val();
ref.child('Blogs/'+user+'/blogs').once('value', function(blogSnapshot) {
var daBlog = blogSnapshot.val();
});
});
You might also want to reconsider if you can restructure your data to better fit your use-case and Firebase's limitations. They have some good documentation on structuring your data, but the most important one for people new to NoSQL/hierarchical databases seems to be "avoid building nests".
Also see my answer on Firebase query if child of child contains a value for a good example. I'd also recommend reading about many-to-many relationships in Firebase, and this article on general NoSQL data modeling.
Given your current data structure you can retrieve the User that contains the blog post you are looking for.
const db = firebase.database()
const usersRef = db.ref('users')
const query = usersRef.orderByChild('blogs/efg').limitToLast(1)
query.once('value').then((ss) => {
console.log(ss.val()) //=> { '7654321': { blogs: {...}}}
})
You need to use limitToLast since Objects are sorted last when using orderByChild docs.
It's actually super easy - just use foreslash:
db.ref('Users').child("userid/name")
db.ref('Users').child("userid/blogs")
db.ref('Users').child("userid/blogs/abc")
No need of loops or anything more.
Related
Given the data structure below in firebase, i want to run a query to retrieve the blog 'efg'. I don't know the user id at this point.
{Users :
"1234567": {
name: 'Bob',
blogs: {
'abc':{..},
'zyx':{..}
}
},
"7654321": {
name: 'Frank',
blogs: {
'efg':{..},
'hij':{..}
}
}
}
The Firebase API only allows you to filter children one level deep (or with a known path) with its orderByChild and equalTo methods.
So without modifying/expanding your current data structure that just leaves the option to retrieve all data and filter it client-side:
var ref = firebase.database().ref('Users');
ref.once('value', function(snapshot) {
snapshot.forEach(function(userSnapshot) {
var blogs = userSnapshot.val().blogs;
var daBlog = blogs['efg'];
});
});
This is of course highly inefficient and won't scale when you have a non-trivial number of users/blogs.
So the common solution to that is to a so-called index to your tree that maps the key that you are looking for to the path where it resides:
{Blogs:
"abc": "1234567",
"zyx": "1234567",
"efg": "7654321",
"hij": "7654321"
}
Then you can quickly access the blog using:
var ref = firebase.database().ref();
ref.child('Blogs/efg').once('value', function(snapshot) {
var user = snapshot.val();
ref.child('Blogs/'+user+'/blogs').once('value', function(blogSnapshot) {
var daBlog = blogSnapshot.val();
});
});
You might also want to reconsider if you can restructure your data to better fit your use-case and Firebase's limitations. They have some good documentation on structuring your data, but the most important one for people new to NoSQL/hierarchical databases seems to be "avoid building nests".
Also see my answer on Firebase query if child of child contains a value for a good example. I'd also recommend reading about many-to-many relationships in Firebase, and this article on general NoSQL data modeling.
Given your current data structure you can retrieve the User that contains the blog post you are looking for.
const db = firebase.database()
const usersRef = db.ref('users')
const query = usersRef.orderByChild('blogs/efg').limitToLast(1)
query.once('value').then((ss) => {
console.log(ss.val()) //=> { '7654321': { blogs: {...}}}
})
You need to use limitToLast since Objects are sorted last when using orderByChild docs.
It's actually super easy - just use foreslash:
db.ref('Users').child("userid/name")
db.ref('Users').child("userid/blogs")
db.ref('Users').child("userid/blogs/abc")
No need of loops or anything more.
Given the data structure below in firebase, i want to run a query to retrieve the blog 'efg'. I don't know the user id at this point.
{Users :
"1234567": {
name: 'Bob',
blogs: {
'abc':{..},
'zyx':{..}
}
},
"7654321": {
name: 'Frank',
blogs: {
'efg':{..},
'hij':{..}
}
}
}
The Firebase API only allows you to filter children one level deep (or with a known path) with its orderByChild and equalTo methods.
So without modifying/expanding your current data structure that just leaves the option to retrieve all data and filter it client-side:
var ref = firebase.database().ref('Users');
ref.once('value', function(snapshot) {
snapshot.forEach(function(userSnapshot) {
var blogs = userSnapshot.val().blogs;
var daBlog = blogs['efg'];
});
});
This is of course highly inefficient and won't scale when you have a non-trivial number of users/blogs.
So the common solution to that is to a so-called index to your tree that maps the key that you are looking for to the path where it resides:
{Blogs:
"abc": "1234567",
"zyx": "1234567",
"efg": "7654321",
"hij": "7654321"
}
Then you can quickly access the blog using:
var ref = firebase.database().ref();
ref.child('Blogs/efg').once('value', function(snapshot) {
var user = snapshot.val();
ref.child('Blogs/'+user+'/blogs').once('value', function(blogSnapshot) {
var daBlog = blogSnapshot.val();
});
});
You might also want to reconsider if you can restructure your data to better fit your use-case and Firebase's limitations. They have some good documentation on structuring your data, but the most important one for people new to NoSQL/hierarchical databases seems to be "avoid building nests".
Also see my answer on Firebase query if child of child contains a value for a good example. I'd also recommend reading about many-to-many relationships in Firebase, and this article on general NoSQL data modeling.
Given your current data structure you can retrieve the User that contains the blog post you are looking for.
const db = firebase.database()
const usersRef = db.ref('users')
const query = usersRef.orderByChild('blogs/efg').limitToLast(1)
query.once('value').then((ss) => {
console.log(ss.val()) //=> { '7654321': { blogs: {...}}}
})
You need to use limitToLast since Objects are sorted last when using orderByChild docs.
It's actually super easy - just use foreslash:
db.ref('Users').child("userid/name")
db.ref('Users').child("userid/blogs")
db.ref('Users').child("userid/blogs/abc")
No need of loops or anything more.
Hi i have a noSql db in firebase.
I want to get the object where userId is 288
i'v tried many combinations but i cant figure out how its done.
This is my code so far :
var refTest= database.ref('conversation')
var query = refTest
.orderByChild('messages');
query.on('value', function(data) {
var a = data.val();
console.log(a.messages.userId);
console.log(data.val());
});
This is a image of my "schema"
I'm obviously a noob when it comes to NoSQL. I do understand SQL
All help is appreciated
You can order/filter on a nested value like this:
var refTest= database.ref('conversation')
var query = refTest.orderByChild('messages/userId').equalTo("288");
query.on('value', function(snapshot) {
snapshot.forEach(function(child) {
console.log(child.key);
console.log(child.val());
});
});
The forEach is needed, since there may be multiple child nodes with messages/userId equal to 288.
The key named "messages" doesn't make sense in your schema. Because if you want to have another message under that conversation, then you wouldn't be able to add it with the same key name and you also couldn't add it under "messages" because it would overwrite the other one. My suggestion is to use the push() method for adding a new message. This way you uniquely identify each message.
Regarding your question, an easy to understand way of parsing your schema is this: you loop through each message of each conversation for finding the messages with userID.
refTest.on('value', function(data) {
var conversations = data.val();
for (conversation in conversations){
for (message in conversation) {
if (message.userId == 288) {
// do whatever you need
// and eventually return something to break the loops
}
}
}
}
Of course, you can adapt it based on your needs
Given the data structure below in firebase, i want to run a query to retrieve the blog 'efg'. I don't know the user id at this point.
{Users :
"1234567": {
name: 'Bob',
blogs: {
'abc':{..},
'zyx':{..}
}
},
"7654321": {
name: 'Frank',
blogs: {
'efg':{..},
'hij':{..}
}
}
}
The Firebase API only allows you to filter children one level deep (or with a known path) with its orderByChild and equalTo methods.
So without modifying/expanding your current data structure that just leaves the option to retrieve all data and filter it client-side:
var ref = firebase.database().ref('Users');
ref.once('value', function(snapshot) {
snapshot.forEach(function(userSnapshot) {
var blogs = userSnapshot.val().blogs;
var daBlog = blogs['efg'];
});
});
This is of course highly inefficient and won't scale when you have a non-trivial number of users/blogs.
So the common solution to that is to a so-called index to your tree that maps the key that you are looking for to the path where it resides:
{Blogs:
"abc": "1234567",
"zyx": "1234567",
"efg": "7654321",
"hij": "7654321"
}
Then you can quickly access the blog using:
var ref = firebase.database().ref();
ref.child('Blogs/efg').once('value', function(snapshot) {
var user = snapshot.val();
ref.child('Blogs/'+user+'/blogs').once('value', function(blogSnapshot) {
var daBlog = blogSnapshot.val();
});
});
You might also want to reconsider if you can restructure your data to better fit your use-case and Firebase's limitations. They have some good documentation on structuring your data, but the most important one for people new to NoSQL/hierarchical databases seems to be "avoid building nests".
Also see my answer on Firebase query if child of child contains a value for a good example. I'd also recommend reading about many-to-many relationships in Firebase, and this article on general NoSQL data modeling.
Given your current data structure you can retrieve the User that contains the blog post you are looking for.
const db = firebase.database()
const usersRef = db.ref('users')
const query = usersRef.orderByChild('blogs/efg').limitToLast(1)
query.once('value').then((ss) => {
console.log(ss.val()) //=> { '7654321': { blogs: {...}}}
})
You need to use limitToLast since Objects are sorted last when using orderByChild docs.
It's actually super easy - just use foreslash:
db.ref('Users').child("userid/name")
db.ref('Users').child("userid/blogs")
db.ref('Users').child("userid/blogs/abc")
No need of loops or anything more.
I'm implementing an orbit.js adapter for firebase, orbit-firebase.
I'm looking for an efficient way to query for multiple records so that I can resolve relationships between objects e.g. course.participants
{
course: {
'c1': {
participants: ['p1', 'p2']
}
},
participant: {
'p1': {
name: "Jim"
},
'p2': {
name: "Mark"
}
}
}
Given I have the ids 'p1' and 'p2' what's an efficient way to query for both of them?
I can't use a query because I'm using security rules with the participants i.e. the user that's trying to resolve course.participants doesn't have access to all of the participants (bear in mind this is a contrived example).
I'd recommend that you move away from arrays in your JSON structures. These are nothing but pain in real-time, distributed data and don't work particularly well with security rules and situations like this.
Given this structure:
course: {
'c1': {
participants: {
'p1': true, 'p2': true
}
}
}
I could join these fairly easily. You can get a normalized ref that behaves just like a Firebase ref by using Firebase.util's NormalizedCollection:
var ref = new Firebase(...);
var coll = new Firebase.util.NormalizedCollection(
ref.child('course/c1/participants'),
ref.child('participant')
).select('participant.name').ref();
coll.on('child_added', function(snap) {
console.log('participant ' + snap.key(), snap.val());
});
Note that this data structure (sans the array) will also make it simpler to enforce read rules on participant data and the like by allowing you to directly reference the user ids under $courseid/participants/, since they are now keys that can match a $ variable.