MongoDB Delete

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Deleting a Document

At some stage you may want to delete a document from a collection. The format is:

db.collectionName.deleteOne(query_criteria) /* deletes the first document found that matches the query criteria */

db.collectionName.remove(query_criteria) /* deletes all documents found that matches the query criteria */

db.collectionName.remove(query_criteria) /* deletes all documents in a collection (use with care!) */

If you want to drop a collection completely, including any data held in it:

db.collectionName.drop() /* removes a collection completely (use with care!) */

This is equivalent to the SQL command:

DROP TABLE tableName;

Department 40 has closed down completely and should be removed. Note, if you added the duplicate department 40 previously you will have 2 documents:

db.dept.find({deptno:40})

Which should return:

{ "_id" : 40, "deptno" : 40, "dname" : "OPERATIONS", "loc" : "BOSTON" }
{ "_id" : 50, "deptno" : 40, "dname" : "OPERATIONS V2", "loc" : "BOSTON" }

If you use the deleteOne() function, it will likely delete the first record. To delete both documents remove() must be used instead:

db.dept.remove({deptno: 40})

Note, if the query_criteria only returns one document, remove() and deleteOne() will have the same effect.

This is equivalent to the SQL command:

DELETE FROM dept WHERE deptno = 40;

Check that the collection has gone:

db.dept.find({deptno:40})

No documents should be returned.

This concludes the section on manipulating collections. Return to the Workbook.