How to retrieve documents from ArangoDB without knowing the structure?

Problem

If you use a NoSQL database it’s common to retrieve documents with an unknown attribute structure. Furthermore, the amount and types of attributes may differ in documents resulting from a single query. Another problem is that you want to add one ore more attributes to a document.

In Java you are used to work with objects. Regarding the upper requirements it is possible to directly retrieve objects with the same attribute structure as the document out of the database. Adding attributes to an object at runtime could be very messy.

Note: ArangoDB 3.1 and the corresponding Java driver is needed.

Solution

With the latest version of the Java driver of ArangoDB an object called BaseDocument is provided.

The structure is very simple: It only has four attributes:

public class BaseDocument {

    String id;
    String key;
    String revision;
    Map<String, Object> properties;

}

The first three attributes are the system attributes _id, _key and _rev. The fourth attribute is a HashMap. The key always is a String, the value an object. These properties contain all non system attributes of the document.

The map can contain values of the following types:

• Map<String, Object>
• List
• Boolean
• Number
• String
• null

Note: Map and List contain objects, which are of the same types as listed above.

To retrieve a document is similar to the known procedure, except that you use BaseDocument as type.

ArangoDB.Builder arango = new ArangoDB.Builder().builder();
DocumentEntity<BaseDocument> myObject = arango.db().collection("myCollection").getDocument("myDocumentKey", BaseDocument.class);

Other resources

More documentation about the ArangoDB Java driver is available:

• Tutorial: Java in ten minutes
• Java driver at Github
• Example source code
• JavaDoc

Author: gschwab, Mark Vollmary

Tags: #java #driver