Retrieve all predicates of all nodes

Users Dgraph
1

Hi Devs,

I want to retrieve all predicates of all nodes. I know that I can do this with

{
  result (func: has(dgraph.type)) {
    uid
    expand(_all_) {
      uid
    }
  }
}

However, this requires all nodes to have a dgraph.type in order for expand to work. Is there any way of retrieving all triples without the requirement of having all nodes have a type?

One alternative that exists is explicitly stating the predicates:

{
  prop as var(func: has(prop))
  edge as var(func: has(edge))
  
  result (func: uid(prop,edge)) {
    uid
    prop
    edge { uid }
  }
}

But for a huge schema this requires many queries. Is there another way you can think of?

2

Yep, there is a “hack” (not sure if it still works). You can create a “dummy” type in Dgraph with all possible edges. And you gonna use:

{
  result(func: has(anyPred)) {
    uid
    expand(MyDummyType) {
      uid
      expand(MyDummyType)
    }
  }
}

This is useful for datasets that you don’t know the structure and wanna create the Schema Type.

3

I presume this returns only uids that have anyPred, so I need a “seed” predicate that all nodes have like xid or dgraph.type. I’ll give it a try with my 235k predicates schema :smiley:

4

Hehehe, curious as to what are you modelling? Want to brainstorm if that the best way to model.

5

I have loaded the DBpedia RDF graph of Wikipedia (also see Discussion: Wikipedia backed by DGraph - #6 by EnricoMi), which comes with a wide schema when you load the infobox properties. These are user-defined predicates, which obviously is noisy and creates k’s of predicates. It is not a hand-crafted well designed schema, but a dirty real-world graph. Just wanted to have a wide long-tail schema for benchmarking.

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6

For reference, I have put the code to generate the DBpedia dataset online, linked from here: Pre-processing DBpedia dataset for Dgraph

1 Like
7

Hi, I had similar need so I got the schema by making a query to /query with request body schema {}
@MichelDiz would there be any reason I should not do it this way?

8

This way what? Not sure what you mean.

Query for the Schema isn’t related to the topic/issue.

9

@MichelDiz Querying the schema appears to return a list of all predicates.

{
  "data": {
    "schema": [
      {
        "predicate": "NRHP",
        "type": "default"
      },
      {
        "predicate": "actor.dubbing_performances",
        "type": "uid",
        "list": true
      },
      {
        "predicate": "actor.film",
        "type": "uid",
        "count": true,
        "list": true
      },
      {
        "predicate": "addr.city",
        "type": "default"
      },
      {
        "predicate": "addr.country",
        "type": "default"
      },
      {
        "predicate": "addr.housename",
        "type": "default"
      },
      {
        "predicate": "addr.housenumber",
        "type": "default"
      }
...
10

@mr_rustbot I thought at the time that the question was related to a normal block. The Schema query is totally different thing(and a Known thing, so I didn’t suspect that He didn’t know about it I guess). You can’t use the result of a Schema query in any other block as far as I know. So, two different topics.

For sure you will have all predicates available in the cluster from a Schema query, but they have no context. With Schema query you will have a list of all predicates, but the question was related to nodes. All predicates of the given nodes. And nodes have context, its “body/object” that a Schema query don’t bring for us.

11

Hi I want to get all the uid connected to a given uid. I am new to dql and I was trying out this:

{
  result (func: uid($uid$)) {
    uid
    expand(_all_) {
      uid
    }
  }
}

I replace the $uid$ with a uid from dgraph. Can you tell me where I am wrong as it is not returning anything but just the uid itself:

{
  "data": {
    "result": [
      {
        "uid": "0xde261e3"
      }
    ]
  },
  "extensions": {
    "server_latency": {
      "parsing_ns": 72899,
      "processing_ns": 475833,
      "encoding_ns": 65990,
      "assign_timestamp_ns": 803103,
      "total_ns": 1525463
    },
    "txn": {
      "start_ts": 100128,
      "hash": "b88882d7227112d39ffa2aee41239ba5512ef018e0d4ea1552b4fd4f38a32e5e"
    },
    "metrics": {
      "num_uids": {
        "": 1,
        "_total": 2,
        "uid": 1
      }
    }
  }
}
12

For expand(_all_) to work you have to define a schema and assign a type to each uid. Then, dgraph knows which predicates to return for each uid.

When to use node types

Node types are optional, but there are two use cases where actually knowing the list of potential predicates of a node is necessary:

  • …
  • retrieving all the predicates of a given node: this is done using the expand(_all_) feature of DQL.

https://dgraph.io/docs/dql/dql-schema/#when-to-use-node-types

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