What is MapR?

MapR is a complete enterprise-grade distribution for Apache Hadoop. The MapR Data Platform has been developed to improve Hadoop’s reliability, performance, and ease of use. The MapR provides a full Hadoop stack that includes the MapR File System (MapR-FS), the MapR-DB NoSQL database management system, MapR Streams, the MapR Control System (MCS) user interface, and a full family of Hadoop ecosystem projects.

Querying

MapR provides native JSON (JavaScript Object Notation) support to MapR Database. The JSON access layer is known as OJAI(Open JSON Application Interface).

Querying dependency

The workstation must setup MapR client and its certificates and should be able to login to mapr dbshell

Java program setup

The workstation must setup MapR client and its certificates

pom.xml
<dependency>
    <groupId>org.ojai</groupId>
    <artifactId>ojai</artifactId>
</dependency>
<dependency>
    <groupId>com.mapr.db</groupId>
    <artifactId>maprdb</artifactId>
</dependency>

1. Find by id

mapr dbshell> find /datalake/path/to/table/users --c {"$eq":{"_id":"5e1dcaaea97bd2004c3caccf"}}
or 
mapr dbshell> find /datalake/path/to/table/users --q {"$where":{"$and":[{"$eq":{"_id":"5e1dcaaea97bd2004c3caccf"}}]}}
#Sample Java snippets
....
com.mapr.db.Admin admin = MapRDB.newAdmin();
com.mapr.db.Table maprTable = MapRDB.getTable("/datalake/path/to/table/users");
org.ojai.Document doc = maprTable.findById("5e1dcaaea97bd2004c3caccf", fieldPaths={"_id","username","fullname","age","dob"});
....

2. Query with $and and select fields

mapr dbshell> find /datalake/path/to/table/users --q {"$select":["_id","username","fullname","age","dob"],"$where":{"$and":[{"$eq":{"_id":"5e1dcaaea97bd2004c3caccf"}}]}}
#Sample Java snippets
....
import org.ojai.store.QueryCondition.Op;
org.ojai.store.QueryCondition query = MapRDB.newCondition().and().is("_id", Op.EQUAL, "5e1dcaaea97bd2004c3caccf").close().build();
org.ojai.DocumentStream doc = maprTable.find(query, fieldPaths={"_id","username","fullname","age","dob"});
....

3. Query with conditions and orderBy

mapr dbshell> find /datalake/path/to/table/users --q {"$where":{"$and":[{"$ge":{"dob":{"$date":"2000-01-15"}}}]},"$orderby":{"username":"desc"}}
#Sample Java snippets
org.ojai.types.OTimestamp ojaiDOB = new org.ojai.types.OTimestamp("2000-01-15");
org.ojai.store.QueryCondition condition = MapRDB.newCondition().and().is("dob", Op.GREATER_OR_EQUAL, ojaiDOB).close().build();
org.ojai.store.Query query = MapRDB.newQuery().where(condition).orderBy("username","DESC")
org.ojai.DocumentStream docs = maprTable.findQuery(query, fieldPaths={"_id","username","fullname","age","dob"});

4. Query with conditions and limit results

mapr dbshell> find /datalake/path/to/table/users --q {"$where":{"$and":[{"$ge":{"dob":{"$date":"2000-01-15"}}}]},"$limit":10}
#Sample Java snippets
org.ojai.types.OTimestamp ojaiDOB = new org.ojai.types.OTimestamp("2000-01-15");
org.ojai.store.QueryCondition condition = MapRDB.newCondition().and().is("dob", Op.GREATER_OR_EQUAL, ojaiDOB).close().build();
org.ojai.store.Query query = MapRDB.newQuery().where(condition).limit(10)
org.ojai.DocumentStream docs = maprTable.findQuery(query, fieldPaths={"_id","username","fullname","age","dob"});

5. Query with range conditions with $ge,$gt,$le,$lt

mapr dbshell> find /datalake/path/to/table/users --q {"$where":{"$and":[{"$ge":{"dob":{"$date":"2000-01-15"}}},{"$le":{"dob":{"$date":"2005-01-15"}}}]},"$orderby":{"username":"desc"},"$limit":10}
#Sample Java snippets
org.ojai.types.OTimestamp ojaiFromDOB = new org.ojai.types.OTimestamp("2000-01-15");
org.ojai.types.OTimestamp ojaiToDOB = new org.ojai.types.OTimestamp("2005-01-15");
org.ojai.store.QueryCondition condition = MapRDB.newCondition().and().is("dob", Op.GREATER_OR_EQUAL, ojaiFromDOB).is("dob", Op.LESS_OR_EQUAL, ojaiToDOB).close().build();
org.ojai.store.Query query = MapRDB.newQuery().where(condition).orderBy("username","DESC").limit(10)
org.ojai.DocumentStream docs = maprTable.findQuery(query, fieldPaths={"_id","username","fullname","age","dob"});    

6. Query with $or

mapr dbshell> find /datalake/path/to/table/users --q {"$where":{"$or":[{"$le":{"dob":{"$date":"2000-01-15"}}},{"$ge":{"age":{"$number":"20"}}}]},"$orderby":{"username":"desc"},"$limit":10}
#Sample Java snippets
org.ojai.types.OTimestamp ojaiFromDOB = new org.ojai.types.OTimestamp("2000-01-15");
org.ojai.store.QueryCondition condition = MapRDB.newCondition().or().is("dob", Op.GREATER_OR_EQUAL, ojaiFromDOB).is("age", Op.LESS_OR_EQUAL, 20).close().build();
org.ojai.store.Query query = MapRDB.newQuery().where(condition).orderBy("username","DESC").limit(10)
org.ojai.DocumentStream docs = maprTable.findQuery(query, fieldPaths={"_id","username","fullname","age","dob"});