BAEL-5357: Retrieve a Value from MongoDB by Its Key Name (#12005)

2022-04-02 03:01:23 +05:30
parent b1c60e9093
commit 007271ec3b
3 changed files with 236 additions and 0 deletions
@@ -0,0 +1,118 @@
+package com.baeldung.mongo;
+
+import static com.mongodb.client.model.Aggregates.project;
+import static com.mongodb.client.model.Projections.fields;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import org.bson.Document;
+import org.bson.conversions.Bson;
+
+import com.mongodb.BasicDBObject;
+import com.mongodb.DB;
+import com.mongodb.DBCollection;
+import com.mongodb.DBCursor;
+import com.mongodb.MongoClient;
+import com.mongodb.client.MongoDatabase;
+import com.mongodb.client.model.Projections;
+
+public class RetrieveValue {
+
+    private static MongoClient mongoClient;
+    private static MongoDatabase database;
+    private static String testCollectionName;
+    private static String databaseName;
+
+    public static void setUp() {
+        if (mongoClient == null) {
+            mongoClient = new MongoClient("localhost", 27017);
+        }
+
+        databaseName = "baeldung";
+        testCollectionName = "travel";
+
+    }
+
+    public static void retrieveValueUsingFind() {
+
+        DB database = mongoClient.getDB(databaseName);
+        DBCollection collection = database.getCollection(testCollectionName);
+
+        BasicDBObject queryFilter = new BasicDBObject();
+
+        BasicDBObject projection = new BasicDBObject();
+        projection.put("passengerId", 1);
+        projection.put("_id", 0);
+
+        DBCursor dbCursor = collection.find(queryFilter, projection);
+        while (dbCursor.hasNext()) {
+            System.out.println(dbCursor.next());
+        }
+
+    }
+
+    public static void retrieveValueUsingAggregation() {
+
+        ArrayList<Document> response = new ArrayList<>();
+
+        ArrayList<Bson> pipeline = new ArrayList<>(Arrays.asList(
+
+            project(fields(Projections.exclude("_id"), Projections.include("passengerId")))));
+
+        database = mongoClient.getDatabase(databaseName);
+
+        database.getCollection(testCollectionName)
+            .aggregate(pipeline)
+            .allowDiskUse(true)
+            .into(response);
+
+        System.out.println("response:- " + response);
+
+    }
+
+    public static void retrieveValueAggregationUsingDocument() {
+
+        ArrayList<Document> response = new ArrayList<>();
+
+        ArrayList<Document> pipeline = new ArrayList<>(Arrays.asList(new Document("$project", new Document("passengerId", 1L))));
+
+        database = mongoClient.getDatabase(databaseName);
+
+        database.getCollection(testCollectionName)
+            .aggregate(pipeline)
+            .allowDiskUse(true)
+            .into(response);
+
+        System.out.println("response:- " + response);
+
+    }
+
+    public static void main(String args[]) {
+
+        //
+        // Connect to cluster (default is localhost:27017)
+        //
+        setUp();
+
+        //
+        // Fetch the data using find query with projected fields
+        //
+
+        retrieveValueUsingFind();
+
+        //
+        // Fetch the data using aggregate pipeline query with projected fields
+        //
+
+        retrieveValueUsingAggregation();
+
+        //
+        // Fetch the data using aggregate pipeline document query with projected fields
+        //
+
+        retrieveValueAggregationUsingDocument();
+
+    }
+}
+