dgo

Official Dgraph Go 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

• Install
• Using a client
  • Create a client
  • Alter the database
  • Create a transaction
  • Run a mutation
  • Run a query
  • Commit a transaction
  • Setting Metadata Headers
• Development
  • Running tests

Install

go get -u -v github.com/dgraph-io/dgo

Using a client

Create a client

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

conn, err := grpc.Dial("localhost:9080", grpc.WithInsecure())
if err != nil {
  log.Fatal(err)
}
defer conn.Close()
dgraphClient := dgo.NewDgraphClient(api.NewDgraphClient(conn))

Alter the database

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

op := &api.Operation{
  Schema: `name: string @index(exact) .`,
}
err := dgraphClient.Alter(ctx, op)
// Check error

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 *dgo.Txn object. This operation incurs no network overhead.

It is a good practice to call txn.Discard() using a defer statement 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 := dgraphClient.NewTxn()
defer txn.Discard(ctx)

Run a mutation

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

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

type Person struct {
  Uid  string `json:"uid,omitempty"`
  Name string `json:"name,omitempty"`
}

p := Person{
  Uid:  "_:alice",
  Name: "Alice",
}

pb, err := json.Marshal(p)
if err != nil {
  log.Fatal(err)
}

mu := &api.Mutation{
  SetJson: pb,
}
assigned, err := txn.Mutate(ctx, mu)
if err != nil {
  log.Fatal(err)
}

For a more complete example, see GoDoc.

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

Run a query

You can run a query by calling txn.Query(ctx, q). 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(ctx, q, vars) with the variables map as third argument.

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

q := `query all($a: string) {
    all(func: eq(name, $a)) {
      name
    }
  }`

resp, err := txn.QueryWithVars(ctx, q, map[string]string{"$a": "Alice"})
fmt.Println(string(resp.Json))

When running a schema query, the schema response is found in the Schema field of api.Response.

q := `schema(pred: [name]) {
  type
  index
  reverse
  tokenizer
  list
  count
  upsert
  lang
}`

resp, err := txn.Query(ctx, q)
fmt.Println(resp.Schema)

Commit a transaction

A transaction can be committed using the txn.Commit(ctx) 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 := dgraphClient.NewTxn()
// Perform some queries and mutations.

err := txn.Commit(ctx)
if err == y.ErrAborted {
  // Retry or handle error
}

Setting Metadata Headers

Metadata headers such as authentication tokens can be set through the context 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.
md := metadata.New(nil)
md.Append("auth-token", "the-auth-token-value")
ctx := metadata.NewOutgoingContext(context.Background(), md)
dg.Alter(ctx, &op)

Development

Running tests

Make sure you have dgraph installed before you run the tests. This script will run the unit and integration tests.

go test -v ./...