Querying in OJAI Applications

To query MapR-DB JSON tables in your OJAI applications, you use the OJAI Query interface. The typical flow of your application involves creating a connection, obtaining a handle to the MapR-DB JSON table you want to query, constructing the query, performing the query, and then processing the results.

Description

The DocumentStore interface includes a Query interface. The Query interface allows you to build a query programmatically.

To construct an OJAI query, call the following methods in the Query interface:

To run the query, pass the Query object to the DocumentStore.findQuery method.

NOTE: Beginning with MapR version 6.0, the MapR-DB Table interface is deprecated and replaced by the OJAI version 2.0 DocumentStore interface.

Basic Application Flow

The following steps describe the basics in developing client applications that query MapR-DB JSON tables using the OJAI API.

Create a Connection instance to your MapR cluster using the DriverManager class:
```
Connection connection = DriverManager.getConnection("ojai:mapr:");
```
NOTE: Do not omit the ending colon in the connection string.
Obtain a DocumentStore handle to a MapR-DB JSON table using the connection object:
```
DocumentStore store = connection.getStore(tablePath);
```
Create a Query object using the connection object:
```
Query query = connection.newQuery();
```

Perform the query operation on the table:

DocumentStream stream = store.findQuery(query);

Process the results.
The following code snippet iterates through the DocumentStream and prints each document as a JSON string:
```
for (final Document userDocument : stream) {
    // Print the OJAI Document
    System.out.println(userDocument.asJsonString());
}
```
To process individual fields within a document, use the DocumentReader interface. The following code snippet iterates through the fields in a document and prints the fields that are strings:
```
Iterable it = stream.documentReaders();
for (DocumentReader reader : it) {
    EventType et = null;
    while ((et = reader.next()) != null) {
        if (et == EventType.STRING) {
            System.out.println("Value of field " + reader.getFieldName() + ": " + reader.getString());
        }
    }
}
```
Close the stream, the connection to the document store, and the connection to MapR:
```
stream.close();
store.close;
connection.close();
```

See Examples: Querying JSON Documents for complete code examples.