Official Dgraph client implementation for Python (Python >= v2.7 and >= v3.5), using grpc.
This client follows the Dgraph Go client closely.
Before using this client, we highly recommend that you go through docs.dgraph.io, and understand how to run and work with Dgraph.
Install using pip:
pip install pydgraphBuild and run the simple project in the examples folder, which
contains an end-to-end example of using the Dgraph python client. Follow the
instructions in the README of that project.
You can initialize a DgraphClient object by passing it a list of
DgraphClientStub clients as variadic arguments. Connecting to multiple Dgraph
servers in the same cluster allows for better distribution of workload.
The following code snippet shows just one connection.
import pydgraph
client_stub = pydgraph.DgraphClientStub('localhost:9080')
client = pydgraph.DgraphClient(client_stub)To set the schema, create an Operation object, set the schema and pass it to
DgraphClient#alter(Operation) method.
schema = 'name: string @index(exact) .'
op = pydgraph.Operation(schema=schema)
client.alter(op)Operation contains other fields as well, including drop predicate and drop all.
Drop all is useful if you wish to discard all the data, and start from a clean
slate, without bringing the instance down.
# Drop all data including schema from the Dgraph instance. This is a useful
# for small examples such as this since it puts Dgraph into a clean state.
op = pydgraph.Operation(drop_all=True)
client.alter(op)To create a transaction, call DgraphClient#txn() method, which returns a
new Txn object. This operation incurs no network overhead.
It is good practice to call Txn#discard() in a finally block after running
the transaction. Calling Txn#discard() after Txn#commit() is a no-op
and you can call Txn#discard() multiple times with no additional side-effects.
txn = client.txn()
try:
# Do something here
# ...
finally:
txn.discard()
# ...To create a read-only transaction, call DgraphClient#txn(read_only=True).
Read-only transactions are ideal for transactions which only involve queries.
Mutations and commits are not allowed.
txn = client.txn(read_only=True)
try:
# Do some queries here
# ...
finally:
txn.discard()
# ...To create a read-only transaction that executes best-effort queries, call
DgraphClient#txn(read_only=True, best_effort=True). Best-effort queries are
faster than normal queries because they bypass the normal consensus protocol.
For this same reason, best-effort queries cannot guarantee to return the latest
data. Best-effort queries are only supported by read-only transactions.
Txn#mutate(mu=Mutation) runs a mutation. It takes in a Mutation object,
which provides two main ways to set data: JSON and RDF N-Quad. You can choose
whichever way is convenient.
Txn#mutate() provides convenience keyword arguments set_obj and del_obj
for setting JSON values and set_nquads and del_nquads for setting N-Quad
values. See examples below for usage.
We define a person object to represent a person and use it in a transaction.
# Create data.
p = {
'name': 'Alice',
}
# Run mutation.
txn.mutate(set_obj=p)
# If you want to use a mutation object, use this instead:
# mu = pydgraph.Mutation(set_json=json.dumps(p).encode('utf8'))
# txn.mutate(mu)
# If you want to use N-Quads, use this instead:
# txn.mutate(set_nquads='_:alice <name> "Alice" .')# Delete data.
query = """query all($a: string)
{
all(func: eq(name, $a))
{
uid
}
}"""
variables = {'$a': 'Bob'}
res = txn.query(query, variables=variables)
ppl = json.loads(res.json)
# For a mutation to delete a node, use this:
txn.mutate(del_obj=person)For a complete example with multiple fields and relationships, look at the
simple project in the examples folder.
Sometimes, you only want to commit a mutation, without querying anything further.
In such cases, you can set the keyword argument commit_now=True to indicate
that the mutation must be immediately committed.
A mutation can be executed using txn.do_request as well.
mutation = txn.create_mutation(set_nquads='_:alice <name> "Alice" .')
request = txn.create_request(mutations=[mutation], commit_now=True)
txn.do_request(request)You can run a query by calling Txn#query(string). You will need to pass in a
GraphQL+- query string. If you want to pass an additional dictionary of any
variables that you might want to set in the query, call
Txn#query(string, variables=d) with the variables dictionary d.
The response would contain the field json, which returns the response JSON.
Let’s run a query with a variable $a, deserialize the result from JSON and
print it out:
# Run query.
query = """query all($a: string) {
all(func: eq(name, $a))
{
name
}
}"""
variables = {'$a': 'Alice'}
res = txn.query(query, variables=variables)
# If not doing a mutation in the same transaction, simply use:
# res = client.txn(read_only=True).query(query, variables=variables)
ppl = json.loads(res.json)
# Print results.
print('Number of people named "Alice": {}'.format(len(ppl['all'])))
for person in ppl['all']:
print(person)This should print:
Number of people named "Alice": 1
AliceYou can also use txn.do_request function to run the query.
request = txn.create_request(query=query)
txn.do_request(request)The txn.do_request function allows you to run upserts consisting of one query and
one mutation. Query variables could be defined and can then be used in the mutation.
To know more about upsert, we highly recommend going through the docs at https://docs.dgraph.io/mutations/#upsert-block.
query = """{
u as var(func: eq(name, "Alice"))
}"""
nquad = """
uid(u) <age> "25" .
"""
cond = "@if(eq(len(u), 1))"
mutation = txn.create_mutation(set_nquads=nquad, cond=cond)
request = txn.create_request(query=query, mutations=[mutation], commit_now=True)
txn.do_request(request)A transaction can be committed using the Txn#commit() method. If your transaction
consisted solely of calls to Txn#query or Txn#queryWithVars, and no calls to
Txn#mutate, then calling Txn#commit() is not necessary.
An error is raised if another transaction(s) modify the same data concurrently that was modified in the current transaction. It is up to the user to retry transactions when they fail.
txn = client.txn()
try:
# ...
# Perform any number of queries and mutations
# ...
# and finally...
txn.commit()
except Exception as e:
if isinstance(e, pydgraph.AbortedError):
# Retry or handle exception.
else:
raise e
finally:
# Clean up. Calling this after txn.commit() is a no-op
# and hence safe.
txn.discard()To clean up resources, you have to call DgraphClientStub#close() individually for
all the instances of DgraphClientStub.
SERVER_ADDR = "localhost:9080"
# Create instances of DgraphClientStub.
stub1 = pydgraph.DgraphClientStub(SERVER_ADDR)
stub2 = pydgraph.DgraphClientStub(SERVER_ADDR)
# Create an instance of DgraphClient.
client = pydgraph.DgraphClient(stub1, stub2)
# ...
# Use client
# ...
# Clean up resources by closing all client stubs.
stub1.close()
stub2.close()Metadata headers such as authentication tokens can be set through the metadata of gRPC methods. Below is an example of how to set a header named "auth-token".
# The following piece of code shows how one can set metadata with
# auth-token, to allow Alter operation, if the server requires it.
# metadata is a list of arbitrary key-value pairs.
metadata = [("auth-token", "the-auth-token-value")]
dg.alter(op, metadata=metadata)- simple: Quickstart example of using pydgraph.
python setup.py install
# To install for the current user, use this instead:
# python setup.py install --userIf you have made changes to the pydgraph/proto/api.proto file, you need need
to regenerate the source files generated by Protocol Buffer tools. To do that,
install the grpcio-tools library and then run the following
command:
python scripts/protogen.pyTo run the tests in your local machine, you can run the script
scripts/local-tests.sh. This script assumes Dgraph and dgo (Go client) are
already built on the local machine. The script will take care of bringing up a
Dgraph cluster and bringing it down after the tests are executed. The script
uses the port 9180 by default to prevent interference with clusters running on
the default port. Docker and docker-compose need to be installed before running
the script. Refer to the official Docker documentation for instructions on how
to install those packages.
The test.sh script downloads and installs Dgraph. It is meant for use by our
CI systems and using it for local development is not recommended.