eliasdb/graphql.md

EliasDB GraphQL

EliasDB supports GraphQL to search nodes in a partition of the graph database. A simple GraphQL query has the following structure:

{
  <node kind> : {
    <attr1>
    <attr2>
    <attr3>
  }
}

It reads: "Get all graph nodes of a certain node kind and fetch attr1, attr2 and attr3 of every node".

Filtering results

It is possible to reduce the number of resulting nodes by defining a condition using the matches argument. For example to get all Person nodes which start with the letters Jo you could write:

query {
  Person(matches: {
    name : "^Jo.*"
  }) {
    name
  }
}

The condition can be inverted by prefixing with not_ so to get all Person nodes which do NOT start with Jo you could write:

query {
  Person(matches: {
    not_name : "^Jo.*"
  }) {
    name
  }
}

To retrieve a specific node with a known key it is possible to do a direct lookup by key:

query {
  Person(key: "john") {
    name
  }
}

Sorting and limiting

To manage potentially large results and avoid overwhelming a client with data it is possible to sort and limit the result.

To sort a result in ascending or descending order use the arguments ascending or descending with the ordering attribute. To order all Person nodes by ascending name write:

query {
  Person(ascending: "name") {
    name
  }
}

To limit the result to the last n entries use the argument last. To limit the result to a range use from to define the start position (default is 0) and items to define how many entries should be returned:

query {
  Person(ascending: "name", last:10) {
    name
  }
}

Traversal

To traverse the graph you need to add the traverse argument on a field of the selection set. For example to get the friends of a Person write:

query {
  Person(ascending: "name") {
    name
    friends(traverse: ":Friend::Person") {
      name
    }
  }
}

Data modification

If the endpoint support mutation of data then you can store and remove nodes and edges. Node and edge storage (create or update) requires all attributes to be specified (nodes and edges are overwritten):

mutation {
  Person(storeNode: {
      key: "hans"
      name: "Hans"
    }) {
    name
    friends(traverse: ":Friend::Person") {
      name
    }
  }
}

Possible arguments are storeNode, storeEdge, removeNode and removeEdge. Removal of nodes and edges requires only the key and kind to be specified. The operation allows retrieval of nodes as well (i.e. the single operation will insert AND retrieve data).

Subscription to updates

EliasDB's implementation of GraphQL supports also subscriptions which involve using Websockets for bidirectional communication. See the examples for further details (in code). A subscription is basically a normal query for example:

subscription {
  Person(ascending: "name") {
    name
  }
}

which receives continuous from the server as the underlying data changes.