SmartGraph Management

This chapter describes the JavaScript interface for creating and modifying SmartGraphs. A SmartGraph is a specialized version of a General Graph, which means all of the General Graph functionality is available on a SmartGraph as well. The major difference of both modules is handling of the underlying collections:

• General Graphs do not enforce or maintain any sharding of the collections and can therefore combine arbitrary sets of existing collections.
• SmartGraphs enforce and rely on a special sharding of the underlying collections and hence can only work with collections that are created through the SmartGraph itself. This also means that SmartGraphs cannot be overlapping. A collection can either be sharded for one SmartGraph or for another. If you need to make sure that all queries can be executed with SmartGraph performance, just create one large SmartGraph covering everything and query it stating the subset of edge collections explicitly.

To generally understand the concept of this module please read the chapter about General Graph Management first. In the following we will only describe the overloaded functionality. Everything else works identical in both modules.

Create a Graph

SmartGraphs require edge relations to be created. The format of the relations is identical to the format used for General Graphs. The only difference is that all collections used within the relations to create a new SmartGraph must not exist yet. You have to let the SmartGraph module create the Graph collections for you, so that it can enforce the correct sharding.

graph_module._create(graphName, edgeDefinitions, orphanCollections, smartOptions)

• graphName (string): Unique identifier of the graph
• edgeDefinitions (array): List of relation definition objects, may be empty
• orphanCollections (array): List of additional vertex collection names, may be empty
• smartOptions (object): A JSON object having the following keys:
  • numberOfShards (number): The number of shards that will be created for each collection. To maintain the correct sharding all collections need an identical number of shards. This cannot be modified after creation of the graph.
  • smartGraphAttribute (string): The attribute that will be used for sharding: vertices with the same value of this attribute will be in the same shard. All vertices are required to have this attribute set and it has to be a string. Edges derive the attribute from their connected vertices.
  • isDisjoint (bool, optional): If set to true, a Disjoint SmartGraph will be created. This flag is not editable after creation. Default: false.
  • satellites (array, optional): An array of collection names that will be used to create SatelliteCollections for a Hybrid (Disjoint) SmartGraph. Each array element must be a string and a valid collection name. The collection type cannot be modified later.

The creation of a graph requires the name and some SmartGraph options. Due to the API edgeDefinitions and orphanCollections have to be given, but both can be empty arrays and be added later.

The edgeDefinitions can be created using the convenience method _relation known from the general-graph module, which is also available here.

orphanCollections again is just a list of additional vertex collections which are not yet connected via edges but should follow the same sharding to be connected later on. Note that these collections are not necessarily orphans in the graph theoretic sense: it is possible to add edges having one end in a collection that has been declared as orphan.

All collections used within the creation process are newly created. The process will fail if one of them already exists, unless they have the correct sharding already. All newly created collections will immediately be dropped again in the failure case.

Examples

Create a graph without relations. Edge definitions can be added later:

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var graph = graph_module._create("myGraph", [], [], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph_module._graph("myGraph");

{[SmartGraph] 
}

Create a graph using an edge collection edges and a single vertex collection vertices as relation:

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var edgeDefinitions = [ graph_module._relation("edges", "vertices", "vertices") ];
arangosh> var graph = graph_module._create("myGraph", edgeDefinitions, [], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph_module._graph("myGraph");

{[SmartGraph] 
  "edges" : [ArangoCollection 10406, "edges" (type edge, status loaded)], 
  "vertices" : [ArangoCollection 10396, "vertices" (type document, status loaded)] 
}

Create a graph with edge definitions and orphan collections:

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var edgeDefinitions = [ graph_module._relation("myRelation", ["male", "female"], ["male", "female"]) ];
arangosh> var graph = graph_module._create("myGraph", edgeDefinitions, ["sessions"], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph_module._graph("myGraph");

{[SmartGraph] 
  "myRelation" : [ArangoCollection 10458, "myRelation" (type edge, status loaded)], 
  "female" : [ArangoCollection 10457, "female" (type document, status loaded)], 
  "male" : [ArangoCollection 10456, "male" (type document, status loaded)], 
  "sessions" : [ArangoCollection 10446, "sessions" (type document, status loaded)] 
}

Modify a graph definition at runtime

After you have created a SmartGraph its definition is not immutable. You can still add or remove relations. This is again identical to General Graphs.

However there is one important difference: you can only add collections that either do not exist, or that have been created by this graph earlier. The latter can be the case if you, for example, remove an orphan collection from this graph, without dropping the collection itself. When after some time you decide to add it to the graph again, you can do it. This is because the enforced sharding is still applied to this vertex collection.

Remove a vertex collection

Remove a vertex collection from the graph:

graph._removeVertexCollection(vertexCollectionName, dropCollection)

• vertexCollectionName (string): Name of vertex collection.
• dropCollection (bool, optional): If true, the collection will be dropped if it is not used in any other graph. Default: false.

In most cases this function works identically to the General Graph one. However there is one special case: The first vertex collection added to the graph (either orphan or within a relation) defines the sharding for all collections within the graph. Every other collection has its distributeShardsLike attribute set to the name of the initial collection. This collection cannot be dropped as long as other collections follow its sharding (i.e. they need to be dropped first).

Examples

Create a SmartGraph and list its orphan collections:

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var relation = graph_module._relation("edges", "vertices", "vertices");
arangosh> var graph = graph_module._create("myGraph", [relation], ["other"], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph._orphanCollections();

[ 
  "other" 
]

Remove the orphan collection from the SmartGraph and drop the collection:

arangosh> graph._removeVertexCollection("other", true);
arangosh> graph_module._graph("myGraph");

{[SmartGraph] 
  "edges" : [ArangoCollection 10712, "edges" (type edge, status loaded)], 
  "vertices" : [ArangoCollection 10701, "vertices" (type document, status loaded)] 
}

Attempting to remove a non-orphan collection results in an error:

arangosh> graph._removeVertexCollection("vertices");

[ArangoError 1928: collection is not in list of orphan collections]

You cannot drop the initial collection (vertices) as long as it defines the sharding for other collections (edges).

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var relation = graph_module._relation("edges", "vertices", "vertices");
arangosh> var graph = graph_module._create("myGraph", [relation], [], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph._deleteEdgeDefinition("edges");
arangosh> graph._removeVertexCollection("vertices");
arangosh> db._drop("vertices");

[ArangoError 1485: Collection 'vertices' must not be dropped while '_local_edges', '_from_edges', '_to_edges', 'edges' have distributeShardsLike set to 'vertices'.]

You may drop the complete graph, but remember to drop collections that you might have removed from the graph beforehand, as they will not be part of the graph definition anymore and thus not be dropped automatically. Alternatively, you can truncate all collections from the graph if you just want to get rid of the data.

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var relation = graph_module._relation("edges", "vertices", "vertices");
arangosh> var graph = graph_module._create("myGraph", [relation], [], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph._deleteEdgeDefinition("edges");
arangosh> graph._removeVertexCollection("vertices");
arangosh> graph_module._drop("myGraph", true); // does not drop any collections
arangosh> db._drop("edges"); // drop before sharding-defining 'vertices' collection
arangosh> db._drop("vertices");

Remove an edge collection

Delete an edge definition from the graph:

graph._deleteEdgeDefinition(edgeCollectionName, dropCollection)

• edgeCollectionName (string): Name of edge collection.
• dropCollection (bool, optional): If true the collection will be dropped if it is not used in any other graph. Default: false.

Examples

Create a SmartGraph, then delete the edge definition and drop the edge collection:

arangosh> var graph_module = require("@arangodb/smart-graph");
arangosh> var relation = graph_module._relation("edges", "vertices", "vertices");
arangosh> var graph = graph_module._create("myGraph", [relation], [], {smartGraphAttribute: "region", numberOfShards: 9});
arangosh> graph._deleteEdgeDefinition("edges", true);
arangosh> graph_module._graph("myGraph");

{[SmartGraph] 
  "vertices" : [ArangoCollection 10901, "vertices" (type document, status loaded)] 
}

It is allowed to remove the vertex collection vertices if it is not used in any relation (i.e. after the deletion of the edge definition):

arangosh> graph._deleteEdgeDefinition("edges");
arangosh> graph._removeVertexCollection("vertices");

Keep in mind that you cannot drop the vertices collection until no other collection references it anymore (distributeShardsLike collection property).

Remove a Graph

Remove a SmartGraph:

graph_module._drop(graphName, dropCollections)

• graphName (string): Name of the Graph.
• dropCollections (bool, optional): Define if collections should be dropped. Default: false.

Examples

Delete a SmartGraph and drop its collections:

arangosh> graph_module._drop("myGraph", true);

Note that removing a Graph with the option to drop the collections fails if you removed collections from the Graph but did not drop these collections. This is because their distributeShardsLike attribute still references collections that are part of the Graph. Dropping collections while others point to them in this way is not allowed. Make sure to drop the referencing collections first.

arangosh> graph._removeVertexCollection("other");
arangosh> graph_module._drop("myGraph", true);

[ArangoError 1485: Collection 'vertices' must not be dropped while 'other' has distributeShardsLike set to 'vertices'.]