Database
The database service allows you to run CRUD operations to your Firebase Realtime Database, and also perform complex queries while doing so.
# Create database instance
db = firebaseApp.database()
Build Path
You can build paths to your data by using the child()
method.
db.child("users").child("Edward")
# Alternate ways
db.child("users", "Edward")
db.child("users/Edward")
Save Data
push
To save data with a unique, auto-generated, timestamp-based key, use the
push()
method.
data = {"name": "Anthony 'Edward' Stark"}
db.child("users").push(data)
set
To create your own keys use the set()
method. The key in the example
below is “Morty”.
data = {"name": "Anthony 'Edward' Stark"}
db.child("users").child("Edward").set(data)
update
To update data for an existing entry use the update()
method.
db.child("users").child("Edward").update({"name": "Tony Stark"})
remove
To delete data for an existing entry use the remove()
method.
db.child("users").child("Edward").remove()
multi-location updates
You can also perform multi-location
updates
with the update()
method.
data = {
"users/Edward/": {
"name": "Anthony 'Edward' Stark"
},
"users/Pepper/": {
"name": "Virginia 'Pepper' Potts"
}
}
db.update(data)
To perform multi-location writes to new locations we can use the
generate_key()
method.
data = {
"users/"+ref.generate_key(): {
"name": "Anthony 'Edward' Stark"
},
"users/"+ref.generate_key(): {
"name": "Virginia 'Pepper' Potts"
}
}
db.update(data)
Retrieve Data
get
To return data from a path simply call the get()
method.
users = db.child("users").get()
each
Returns a list of objects on each of which you can call val()
and
key()
.
users = db.child("users").get()
for user in users.each():
print(user.key(), user.val())
# Output:
# Edward {name": "Anthony 'Edward' Stark"}
# Pepper {'name': "Virginia 'Pepper' Potts"}
val
Queries return a PyreResponse object. Calling val()
on these objects
returns the query data.
users = db.child('users').child('Edward').get()
for user in users.each():
print(user.val())
# Output:
# {'name': "Anthony 'Edward' Stark"}
key
Calling key()
returns the key for the query data.
users = db.child("users").get()
for user in users.each():
print(user.key())
# Output:
# Edward
# Pepper
Conditional Requests
It’s possible to do conditional sets and removes by using the
conditional_set()
and conitional_remove()
methods respectively.
You can read more about conditional requests in Firebase
here.
To use these methods, you first get the ETag of a particular path by
using the get_etag()
method. You can then use that tag in your
conditional request.
etag = db.child("users").child("Edward").get_etag()
data = {"name": "Tony Stark"}
db.child("users").child("Edward").conditional_set(data, etag)
If the passed ETag does not match the ETag of the path in the database, the data will not be written, and both conditional request methods will return a single key-value pair with the new ETag to use of the following form:
{ "ETag": "8KnE63B6HiKp67Wf3HQrXanujSM=" }
Here’s an example of checking whether or not a conditional removal was successful:
etag = db.child("users").child("Edward").get_etag()
response = db.child("users").child("Edward").conditional_remove(etag)
if "ETag" in response:
etag = response["ETag"] # our ETag was out-of-date
else:
print("We removed the data successfully!")
shallow
To return just the keys at a particular path use the shallow()
method.
all_user_ids = db.child("users").shallow().get()
Note
shallow()
can not be used in conjunction with any complex queries.
streaming
You can listen to live changes to your data with the stream()
method.
def stream_handler(message):
print(message["event"]) # put
print(message["path"]) # /-K7yGTTEp7O549EzTYtI
print(message["data"]) # {'title': 'Firebase', "body": "etc..."}
my_stream = db.child("posts").stream(stream_handler)
You should at least handle put
and patch
events. Refer to
“Streaming from the REST
API”
for details.
You can also add a stream_id
to help you identify a stream if you
have multiple running:
my_stream = db.child("posts").stream(stream_handler, stream_id="new_posts")
close the stream
my_stream.close()
Complex Queries
Queries can be built by chaining multiple query parameters together.
users_by_name = db.child("users").order_by_child("name").limit_to_first(3).get()
This query will return the first three users ordered by name.
order_by_child
We begin any complex query with order_by_child()
.
users_by_name = db.child("users").order_by_child("name").get()
This query will return users ordered by name.
equal_to
Return data with a specific value.
users_by_score = db.child("users").order_by_child("score").equal_to(10).get()
This query will return users with a score of 10.
start_at and end_at
Specify a range in your data.
users_by_score = db.child("users").order_by_child("score").start_at(3).end_at(10).get()
This query returns users ordered by score and with a score between 3 and 10.
limit_to_first and limit_to_last
Limits data returned.
users_by_score = db.child("users").order_by_child("score").limit_to_first(5).get()
This query returns the first five users ordered by score.
order_by_key
When using order_by_key()
to sort your data, data is returned in
ascending order by key.
users_by_key = db.child("users").order_by_key().get()
order_by_value
When using order_by_value()
, children are ordered by their value.
users_by_value = db.child("users").order_by_value().get()
Helper Methods
generate_key
db.generate_key()
is an implementation of Firebase’s key generation
algorithm.
See multi-location updates for a potential use case.
sort
Sometimes we might want to sort our data multiple times. For example, we might want to retrieve all articles written between a certain date then sort those articles based on the number of likes.
Currently the REST API only allows us to sort our data once, so the
sort()
method bridges this gap.
articles = db.child("articles").order_by_child("date").start_at(startDate).end_at(endDate).get()
articles_by_likes = db.sort(articles, "likes")
Common Errors
Index not defined
Indexing is not enabled for the database reference.