github.com/dgraph-io/dgo/v2

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

• Import
• Using a client
  • Creating a client
  • Altering the database
  • Creating a transaction
  • Running a mutation
  • Running a query
  • Running an Upsert: Query + Mutation
  • Running Conditional Upsert
  • Committing a transaction
  • Setting Metadata Headers
• Development
  • Running tests

Import

Depending on the version of Dgraph that you are connecting to, you will have to use a different version of this client and their corresponding import paths.

Dgraph version	dgo version	dgo import path
dgraph 1.0.X	dgo 1.X.Y	"github.com/dgraph-io/dgo"
dgraph 1.1.X	dgo 2.X.Y	"github.com/dgraph-io/dgo/v2"

Note: One of the most important API breakages from dgo v1 to v2 is in the function dgo.Txn.Mutate. This function returns an *api.Assigned value in v1 but an *api.Response in v2.

Using a client

Creating a client

dgraphClient object can be initialized 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))

Altering 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.

Creating 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)

Read-only transactions can be created by calling c.NewReadOnlyTxn(). Read-only transactions are useful to increase read speed because they can circumvent the usual consensus protocol. Read-only transactions cannot contain mutations and trying to call txn.Commit() will result in an error. Calling txn.Discard() will be a no-op.

Running 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.

To use JSON, use the fields SetJson and DeleteJson, which accept a string representing the nodes to be added or removed respectively (either as a JSON map or a list). To use RDF, use the fields SetNquads and DeleteNquads, which accept a string representing the valid RDF triples (one per line) to added or removed respectively. This protobuf object also contains the Set and Del fields which accept a list of RDF triples that have already been parsed into our internal format. As such, these fields are mainly used internally and users should use the SetNquads and DeleteNquads instead if they are planning on using RDF.

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"`
	DType []string `json:"dgraph.type,omitempty"`
}

p := Person{
	Uid:   "_:alice",
	Name:  "Alice",
	DType: []string{"Person"},
}

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

mu := &api.Mutation{
	SetJson: pb,
}
res, 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.

Mutation can be run using txn.Do as well.

mu := &api.Mutation{
  SetJson: pb,
}
req := &api.Request{CommitNow:true, Mutations: []*api.Mutation{mu}}
res, err := txn.Do(ctx, req)
if err != nil {
  log.Fatal(err)
}

Running 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
    }
  }`

res, err := txn.QueryWithVars(ctx, q, map[string]string{"$a": "Alice"})
fmt.Printf("%s\n", res.Json)

You can also use txn.Do function to run a query.

req := &api.Request{
  Query: q,
  Vars: map[string]string{"$a": "Alice"},
}
res, err := txn.Do(ctx, req)
if err != nil {
  log.Fatal(err)
}
fmt.Printf("%s\n", res.Json)

When running a schema query for predicate name, the schema response is found in the Json field of api.Response as shown below:

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

res, err := txn.Query(ctx, q)
if err != nil {
    log.Fatal(err)
}
fmt.Printf("%s\n", res.Json)

Running an Upsert: Query + Mutation

The txn.Do function allows you to run upserts consisting of one query and one mutation. Variables can be defined in the query and used in the mutation. You could also use txn.Do to perform a query followed by a mutation.

To know more about upsert, we highly recommend going through the docs at https://docs.dgraph.io/mutations/#upsert-block.

query = `
  query {
      user as var(func: eq(email, "[e-mail]"))
  }`
mu := &api.Mutation{
  SetNquads: []byte(`uid(user) <email> "[e-mail]" .`),
}
req := &api.Request{
  Query: query,
  Mutations: []*api.Mutation{mu},
  CommitNow:true,
}

// Update email only if matching uid found.
if _, err := dg.NewTxn().Do(ctx, req); err != nil {
  log.Fatal(err)
}

Running Conditional Upsert

The upsert block also allows specifying a conditional mutation block using an @if directive. The mutation is executed only when the specified condition is true. If the condition is false, the mutation is silently ignored.

See more about Conditional Upsert Here.

query = `
  query {
      user as var(func: eq(email, "[e-mail]"))
  }`
mu := &api.Mutation{
  Cond: `@if(eq(len(user), 1))`, // Only mutate if "[e-mail]" belongs to single user.
  SetNquads: []byte(`uid(user) <email> "[e-mail]" .`),
}
req := &api.Request{
  Query: query,
  Mutations: []*api.Mutation{mu},
  CommitNow:true,
}

// Update email only if exactly one matching uid is found.
if _, err := dg.NewTxn().Do(ctx, req); err != nil {
  log.Fatal(err)
}

Committing 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 ./...