Support DQL variables in mutations

Issues Dgraph
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8

+1 for this feature.

Would it be possible to make it more clear in docs that upsert variables aren’t currently supported? (I spent a lot of time trying to debug this today when I came across the problem in pydgraph and then reproduced a minimal example using raw curl requests.)

Minimal Example

Set the schema using GraphQL:

# schema.graphql
type Project {
    id: String! @id
    name: String @search(by: [term])
    description: String @search(by: [term])
}

Create the schema:

curl -X POST localhost:8080/admin/schema --data-binary '@schema.graphql'

Create inital data:

curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d $'
    {
      "set": [
        {
          "Project.id": "06b49118-a34a-4254-b1a1-49e3096676aa",
          "Project.name": "test",
          "Project.description": "test",
          "dgraph.type": "Project"
        },
        {
          "Project.id": "8296209e-9e3e-4170-892f-14ca17281eca",
          "Project.name": "test",
          "Project.description": "test",
          "dgraph.type": "Project"
        }
      ]
    }' | jq

Demonstrate the problem:

First example fails with variable

curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d '
{
  "query": "query foo($id: string) { bar(func: eq(Project.id, $id )) {v as uid} }",
  "delete": {
    "uid": "uid(v)"
  },
  "variables": {"$id": "8296209e-9e3e-4170-892f-14ca17281eca"}
}' | jq

The response bar query is blank:

{
  "data": {
    "code": "Success",
    "message": "Done",
    "queries": {
      "bar": []
    },
    "uids": {}
  },
  "extensions": {
    "server_latency": {
      "parsing_ns": 44507,
      "processing_ns": 837772,
      "encoding_ns": 29162,
      "assign_timestamp_ns": 757242,
      "total_ns": 1750146
    },
    "txn": {
      "start_ts": 21328,
      "commit_ts": 21329
    }
  }
}

Second example works with a hard-coded data

curl -H "Content-Type: application/json" -X POST localhost:8080/mutate?commitNow=true -d '
{
  "query": "query foo($id: string) { bar(func: eq(Project.id, \"8296209e-9e3e-4170-892f-14ca17281eca\" )) {v as uid} }",
  "delete": {
    "uid": "uid(v)"
  },
  "variables": {"$id": "8296209e-9e3e-4170-892f-14ca17281eca"}
}' | jq

The response bar query is populated:

{
  "data": {
    "code": "Success",
    "message": "Done",
    "queries": {
      "bar": [
        {
          "uid": "0x4ec9"
        }
      ]
    },
    "uids": {}
  },
  "extensions": {
    "server_latency": {
      "parsing_ns": 85802,
      "processing_ns": 1154781,
      "encoding_ns": 50707,
      "assign_timestamp_ns": 507082,
      "total_ns": 1828617
    },
    "txn": {
      "start_ts": 21309,
      "commit_ts": 21310,
      "preds": [
        "1-Project.description",
        "1-Project.id",
        "1-Project.name",
        "1-dgraph.type"
      ]
    }
  }
}