Querying with Select
The examples in this section query a document store and retrieve specific fields from the documents.
The following example shows how to retrieve the _id
and
address.zipCode
fields from all documents in a store using the Query.select method.
/**
* Copyright (c) 2017 MapR, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
* an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
* specific language governing permissions and limitations under the License.
*/
package com.mapr.ojai.examples;
import org.ojai.Document;
import org.ojai.DocumentStream;
import org.ojai.store.Connection;
import org.ojai.store.DocumentStore;
import org.ojai.store.DriverManager;
import org.ojai.store.Query;
public class OJAI_006_FindQueryWithSelect {
public static void main(final String[] args) {
System.out.println("==== Start Application ===");
// Create an OJAI connection to MapR cluster
final Connection connection = DriverManager.getConnection("ojai:mapr:");
// Get an instance of OJAI DocumentStore
final DocumentStore store = connection.getStore("/demo_table");
// Build an OJAI query
final Query query = connection.newQuery()
.select("_id", "address.zipCode")
.build();
// fetch all OJAI Documents from this store
final DocumentStream stream = store.find(query);
for (final Document userDocument : stream) {
// Print the OJAI Document
System.out.println(userDocument.asJsonString());
}
// Close this instance of OJAI DocumentStore
store.close();
// close the OJAI connection and release any resources held by the connection
connection.close();
System.out.println("==== End Application ===");
}
}
The following example shows how to retrieve the _id
and
address.zipCode
fields from all documents in a store using an OJAI
query.
/*
* Copyright (c) 2018 MapR, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
const { ConnectionManager } = require('node-maprdb');
const connectionString = 'localhost:5678?' +
'auth=basic;' +
'user=mapr;' +
'password=mapr;' +
'ssl=true;' +
'sslCA=/opt/mapr/conf/ssl_truststore.pem;' +
'sslTargetNameOverride=node1.mapr.com';
let connection;
// Create a connection to data access server
ConnectionManager.getConnection(connectionString)
.then((conn) => {
connection = conn;
// Get a store
return connection.getStore('/demo_table');
})
.then((store) => {
// Create an OJAI query
const query = {"$select": ["_id", "address.zipCode"]};
// fetch OJAI Documents by query
return store.find(query);
})
.then((queryResult) => {
queryResult.on('data', (document) => {
// Print OJAI Documents from document stream
console.log(document);
});
queryResult.on('end', () => {
// close the OJAI connection
connection.close();
});
});
The following example shows how to retrieve the _id
and
address.zipCode
fields from all documents in a store using an OJAI
query.
from mapr.ojai.storage.ConnectionFactory import ConnectionFactory
# Create a connection to data access server
connection_str = "localhost:5678?auth=basic;user=mapr;password=mapr;" \
"ssl=true;" \
"sslCA=/opt/mapr/conf/ssl_truststore.pem;" \
"sslTargetNameOverride=node1.mapr.com"
connection = ConnectionFactory.get_connection(connection_str=connection_str)
# Get a store and assign it as a DocumentStore object
store = connection.get_store('/demo_table')
# Create an OJAI query
query = {"$select": ["_id", "address.zipCode"]}
# options for find request
options = {
'ojai.mapr.query.result-as-document': True
}
# fetch OJAI Documents by query
query_result = store.find(query, options=options)
# Print OJAI Documents from document stream
for doc in query_result:
print(doc.as_dictionary())
# close the OJAI connection
connection.close()
The following two dbshell commands are equivalent to the code examples. See dbshell find or findbyid for more details about the syntax dbshell provides.
# mapr dbshell
maprdb root:> find /demo_table --query {"$select":["_id","address.zipcode"]}
maprdb root:> find /demo_table --fields _id,address.zipcode
The following example shows how to retrieve the _id
and
address.zipCode
fields from all documents in a store using an OJAI
query.
using System;
using MapRDB.Driver;
using MapRDB.Driver.Ojai;
public class FindQueryWithSelect
{
public async void FindQueryWithSelect()
{
// Create a connection to data access server
var connectionStr = $"localhost:5678?auth=basic;" +
$"user=mapr;" +
$"password=mapr;" +
$"ssl=true;" +
$"sslCA=/opt/mapr/conf/ssl_truststore.pem;" +
$"sslTargetNameOverride=node1.mapr.com";
var connection = ConnectionFactory.CreateConnection(connectionStr);
// Get a store and assign it as a DocumentStore object
var store = connection.GetStore("/demo_table");
//Create an OJAI query
var query = connection.NewQuery().Select("_id", "address.zipCode").Build();
// Options for find request
var options = new QueryOptions(1000, true);
// Fetch OJAI Documents by query
var queryResult = store.Find(query, options);
var documentStream = await queryResult.GetDocumentAsyncStream().GetAllDocuments();
// Print OJAI Documents from document stream
foreach (var document in documentStream)
{
Console.WriteLine(document.ToDictionary());
}
// Close the OJAI connection
connection.Close();
}
}
The following example shows how to retrieve the _id
and
address.zipCode
fields from all documents in a store using an OJAI
query.
package main
import (
"fmt"
client "github.com/mapr/private-maprdb-go-client"
)
func main() {
// Create connection string
connectionString := "192.168.33.11:5678?" +
"auth=basic;" +
"user=mapr;" +
"password=mapr;" +
"ssl=true;" +
"sslCA=/opt/mapr/conf/ssl_truststore.pem;" +
"sslTargetNameOverride=node1.cluster.com"
storeName := "/demo_table"
// Create a connection to DAG
connection, err := client.MakeConnection(connectionString)
if err != nil {
panic(err)
}
// Get a store and assign it as a DocumentStore struct
store, err := connection.GetStore(storeName)
if err != nil {
panic(err)
}
// Options for find request
options := &client.FindOptions{ResultAsDocument: true}
// Create an OJAI query
query := map[string]interface{}{"$select": []interface{}{"_id", "address.zipCode"}}
// Fetch all OJAI Documents from table
findResult, err := store.FindQueryMap(query, options)
// Print OJAI Documents from document stream
for _, doc := range findResult.DocumentList() {
fmt.Println(doc)
}
// Close connection
connection.Close()
}