BAEL-5360: Check Collection Existence in MongoDB (#11905)

* BAEL-5360: Check Collection Existence in MongoDB

* BAEL-5360: update test names using the bdd scheme

persistence-modules/java-mongodb/src/main/java/com/baeldung/mongo/CollectionExistence.java

@@ -0,0 +1,100 @@
+package com.baeldung.mongo;
+
+import java.util.ArrayList;
+
+import org.bson.Document;
+
+import com.mongodb.DB;
+import com.mongodb.MongoClient;
+import com.mongodb.client.MongoCollection;
+import com.mongodb.client.MongoDatabase;
+
+public class CollectionExistence {
+
+    private static MongoClient mongoClient;
+
+    private static String testCollectionName;
+    private static String databaseName;
+
+    public static void setUp() {
+        if (mongoClient == null) {
+            mongoClient = new MongoClient("localhost", 27017);
+        }
+        databaseName = "baeldung";
+        testCollectionName = "student";
+    }
+
+    public static void collectionExistsSolution() {
+
+        DB db = mongoClient.getDB(databaseName);
+
+        System.out.println("collectionName " + testCollectionName + db.collectionExists(testCollectionName));
+
+    }
+
+    public static void createCollectionSolution() {
+
+        MongoDatabase database = mongoClient.getDatabase(databaseName);
+
+        try {
+            database.createCollection(testCollectionName);
+
+        } catch (Exception exception) {
+            System.err.println("Collection already Exists");
+        }
+
+    }
+
+    public static void listCollectionNamesSolution() {
+
+        MongoDatabase database = mongoClient.getDatabase(databaseName);
+        boolean collectionExists = database.listCollectionNames()
+            .into(new ArrayList<String>())
+            .contains(testCollectionName);
+
+        System.out.println("collectionExists:- " + collectionExists);
+
+    }
+
+    public static void countSolution() {
+
+        MongoDatabase database = mongoClient.getDatabase(databaseName);
+
+        MongoCollection<Document> collection = database.getCollection(testCollectionName);
+
+        System.out.println(collection.count());
+
+    }
+
+    public static void main(String args[]) {
+
+        //
+        // Connect to cluster (default is localhost:27017)
+        //
+        setUp();
+
+        //
+        // Check the db existence using DB class's method
+        //
+        collectionExistsSolution();
+
+        //
+        // Check the db existence using the createCollection method of MongoDatabase class
+        //
+        createCollectionSolution();
+
+        //
+        // Check the db existence using the listCollectionNames method of MongoDatabase class
+        //
+        listCollectionNamesSolution();
+
+        //
+        // Check the db existence using the count method of MongoDatabase class
+        //
+        countSolution();
+
+    }
+
+}
+
+

persistence-modules/java-mongodb/src/test/java/com/baeldung/mongo/CollectionExistenceLiveTest.java

@@ -0,0 +1,98 @@
+package com.baeldung.mongo;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+
+import org.bson.Document;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.mongodb.DB;
+import com.mongodb.MongoClient;
+import com.mongodb.client.MongoCollection;
+import com.mongodb.client.MongoDatabase;
+
+public class CollectionExistenceLiveTest {
+
+    private MongoClient mongoClient;
+    private String testCollectionName;
+    private String databaseName;
+
+    @Before
+    public void setup() {
+        if (mongoClient == null) {
+            mongoClient = new MongoClient("localhost", 27017);
+            databaseName = "baeldung";
+            testCollectionName = "student";
+
+            // Create a new collection if it doesn't exists.
+            try {
+                MongoDatabase database = mongoClient.getDatabase(databaseName);
+                database.createCollection(testCollectionName);
+
+            } catch (Exception exception) {
+
+                System.out.println("Collection already Exists");
+            }
+
+        }
+    }
+
+    @Test
+    public void givenCreateCollection_whenCollectionAlreadyExists_thenCheckingForCollectionExistence() {
+
+        MongoDatabase database = mongoClient.getDatabase(databaseName);
+        Boolean collectionStatus = false;
+        Boolean expectedStatus = true;
+
+        try {
+            database.createCollection(testCollectionName);
+
+        } catch (Exception exception) {
+            collectionStatus = true;
+            System.err.println("Collection already Exists");
+        }
+
+        assertEquals(expectedStatus, collectionStatus);
+
+    }
+
+    @Test
+    public void givenCollectionExists_whenCollectionAlreadyExists_thenCheckingForCollectionExistence() {
+
+        DB db = mongoClient.getDB(databaseName);
+        Boolean collectionStatus = db.collectionExists(testCollectionName);
+
+        Boolean expectedStatus = true;
+        assertEquals(expectedStatus, collectionStatus);
+
+    }
+
+    @Test
+    public void givenListCollectionNames_whenCollectionAlreadyExists_thenCheckingForCollectionExistence() {
+
+        MongoDatabase database = mongoClient.getDatabase(databaseName);
+        boolean collectionExists = database.listCollectionNames()
+            .into(new ArrayList<String>())
+            .contains(testCollectionName);
+
+        Boolean expectedStatus = true;
+        assertEquals(expectedStatus, collectionExists);
+
+    }
+
+    @Test
+    public void givenCount_whenCollectionAlreadyExists_thenCheckingForCollectionExistence() {
+
+        MongoDatabase database = mongoClient.getDatabase(databaseName);
+
+        MongoCollection<Document> collection = database.getCollection(testCollectionName);
+        Boolean collectionExists = collection.count() > 0 ? true : false;
+
+        Boolean expectedStatus = false;
+        assertEquals(expectedStatus, collectionExists);
+
+    }
+}
+