dgraph 0.4.0

Dgraph Dart client which communicates with the server using gRPC.

dgraph

Dgraph Dart client which communicates with the server using gRPC.

Before using this client, we highly recommend that you go through tour.dgraph.io and docs.dgraph.io to understand how to run and work with Dgraph.

Table of contents

• dgraph
  • Table of contents
  • Using a client
    • Create a client
    • Alter the database
    • Create a transaction
    • Run a mutation
    • Run a query
    • Commit a transaction

Using a client

Create a client

dgraphClient object can be initialised by passing it a list of api.DgraphApi 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.

DgraphRpcClient rpcClient =
    DgraphRpcClient("localhost", 9080, const ChannelCredentials.insecure());
Dgraph dgraphClient = dgraph.NewDgraphClient(api.DgraphApi(rpcClient));

Alter the database

To set the schema, create an instance of api.Operation and use the Alter endpoint.

api.Operation operation = api.Operation();
operation.schema = """
name: string @index(exact) .
""";
await dgraphClient.Alter(clientContext, operation);

Operation contains other fields as well, including dropAttr and dropAll. dropAll is useful if you wish to discard all the data, and start from a clean slate, without bringing the instance down. dropAttr is used to drop all the data related to a predicate.

Create a transaction

To create a transaction, call dgraphClient.NewTxn(), which returns a Txn object. This operation incurs no network overhead.

It is a good practice to call txn.Discard() on a finally block after it is initialized. Calling txn.Discard() after txn.Commit() is a no-op and you can call txn.Discard() multiple times with no additional side-effects.

Txn txn;
ClientContext clientContext = ClientContext();
try {
  txn = dgraphClient.NewTxn();
  // Perform some queries and mutations.
  // Commit the transaction.
} finally {
  txn.Discard(clientContext);
}

Run a mutation

txn.Mutate(clientContext, mutation) runs a mutation. It takes in a ClientContext and a api.Mutation object. You can set the data using JSON or RDF N-Quad format.

We define a Map to represent a Person and convert an instance of it to use with Mutation object.

Map<String, dynamic> p = {
  "uid": "_:alice",
  "name": "Alice",
};
List<int> pb = utf8.encode(json.encode(p));
api.Mutation mutation = api.Mutation();
mutation.setJson = pb;
api.Assigned assigned = await txn.Mutate(clientContext, mutation);
print("Assigned: $assigned");
// uids: {alice : 0x1}

Sometimes, you only want to commit a mutation, without querying anything further. In such cases, you can use mutation.commitNow = true to indicate that the mutation must be immediately committed.

Run a query

You can run a query by calling txn.Query(clientContext, query). You will need to pass in a GraphQL+- query string. If you want to pass an additional map of any variables that you might want to set in the query, call txn.QueryWithVars(clientContext, query, vars) with the variables map as third argument.

Let's run the following query with a variable $a:

String query = """
query all(\$a: string) {
  all(func: eq(name, \$a)) {
    name
  }
}
""";
api.Response response =
    await txn.QueryWithVars(clientContext, query, {"\$a": "Alice"});
print(
    "Response: ${latin1.decode(base64.decode(json.decode(response.writeToJson())['1']))}");
// {"all":[{"name":"Alice"}]}

Commit a transaction

A transaction can be committed using the txn.Commit(clientContext) 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 will be returned if other transactions running concurrently modify the same data that was modified in this transaction. It is up to the user to retry transactions when they fail.

Txn txn;
ClientContext clientContext = ClientContext();
try {
  txn = dgraphClient.NewTxn();
  // Perform some queries and mutations.
  txn.Commit(clientContext);
} catch (e) {
  // Retry or handle error
}