Query Variables in DQL

Syntax Examples:

varName as q(func: ...) { ... }
varName as var(func: ...) { ... }
varName as predicate { ... }
varName as predicate @filter(...) { ... }

Types : uid

Nodes (UIDs) matched at one place in a query can be stored in a variable and used elsewhere. Query variables can be used in other query blocks or in a child node of the defining block.

Query variables do not affect the semantics of the query at the point of definition. Query variables are evaluated to all nodes matched by the defining block.

In general, query blocks are executed in parallel, but variables impose an evaluation order on some blocks. Cycles induced by variable dependence are not permitted.

If a variable is defined, it must be used elsewhere in the query.

A query variable is used by extracting the UIDs in it with uid(var-name).

The syntax func: uid(A,B) or @filter(uid(A,B)) means the union of UIDs for variables A and B.

Query Example: The movies of Angelia Jolie and Brad Pitt where both have acted on movies in the same genre. Note that B and D match all genres for all movies, not genres per movie.

{
 var(func:allofterms(name@en, "angelina jolie")) {
   actor.film {
    A AS performance.film {  # All films acted in by Angelina Jolie
     B As genre  # Genres of all the films acted in by Angelina Jolie
    }
   }
  }

 var(func:allofterms(name@en, "brad pitt")) {
   actor.film {
    C AS performance.film {  # All films acted in by Brad Pitt
     D as genre  # Genres of all the films acted in by Brad Pitt
    }
   }
  }

 films(func: uid(D)) @filter(uid(B)) {   # Genres from both Angelina and Brad
  name@en
   ~genre @filter(uid(A, C)) {  # Movies in either A or C.
     name@en
   }
 }
}

curl localhost:8080/query -XPOST -d '
blahblah' | python -m json.tool | less

package main

import (
	"context"
	"flag"
	"fmt"
	"log"
    
	"github.com/dgraph-io/dgo"
	"github.com/dgraph-io/dgo/protos/api"
    
	"google.golang.org/grpc"
)

var (
	dgraph = flag.String("d", "127.0.0.1:9080", "Dgraph Alpha address")
)

func main() {
	flag.Parse()
	conn, err := grpc.Dial(*dgraph, grpc.WithInsecure())
	if err != nil {
		log.Fatal(err)
	}
	defer conn.Close()

	dg := dgo.NewDgraphClient(api.NewDgraphClient(conn))
    
	resp, err := dg.NewTxn().Query(context.Background(), `blahblah`)
	
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("Response: %s\n", resp.Json)
}

import io.dgraph.DgraphClient;
import io.dgraph.DgraphGrpc;
import io.dgraph.DgraphGrpc.DgraphStub;
import io.dgraph.DgraphProto.Response;
import io.grpc.ManagedChannel;
import io.grpc.ManagedChannelBuilder;

import java.util.Map;

public class App {

    public static void main(final String[] args) {
        ManagedChannel channel =
            ManagedChannelBuilder.forAddress("localhost", 9080).usePlaintext(true).build();
        DgraphStub stub = DgraphGrpc.newStub(channel);
        DgraphClient dgraphClient = new DgraphClient(stub);

        String query = "blahblah";

    
        Response res = dgraphClient.newTransaction().query(query);
    
        System.out.printf("Response: %s", res.getJson().toStringUtf8());
    }
}

import pydgraph
import json

def main():
    client_stub = pydgraph.DgraphClientStub("localhost:9080")
    client = pydgraph.DgraphClient(client_stub)
    query = """blahblah"""
    res = client.txn(read_only=True).query(query)
    print('Response: {}'.format(json.loads(res.json)))

    client_stub.close()


if __name__ == '__main__':
    try:
        main()
    except Exception as e:
        print('Error: {}'.format(e))

const dgraph = require("dgraph-js");
const grpc = require("grpc");

async function main() {
  const clientStub = new dgraph.DgraphClientStub("localhost:9080", grpc.credentials.createInsecure());
  const dgraphClient = new dgraph.DgraphClient(clientStub);

  const query = `blahblah`;
  const response = await dgraphClient.newTxn().query(query);
  console.log("Response: ", JSON.stringify(response.getJson()));

  clientStub.close();
}

main().then().catch((e) => {
  console.log("ERROR: ", e);
});

const dgraph = require("dgraph-js-http");

async function main() {
  const clientStub = new dgraph.DgraphClientStub("http://localhost:8080");
  const dgraphClient = new dgraph.DgraphClient(clientStub);

  const query = `blahblah`;
  const response = await dgraphClient.newTxn().query(query);
  console.log("Response: ", JSON.stringify(response.data));
}

main().then().catch((e) => {
  console.log("ERROR: ", e);
});