MongoDB Update

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Updating a Collection

The format of the update command is:

 db.collectionName.update({'keyField': 'value' }, 
  {$set: field: 'newValue' }
 )

The update() function can be used to update one or more documents. If the change should only apply to one document, the keyField needs to be a field with unique values, to ensure the correct document is updated.

This is similar in SQL to proving the WHERE clause of an UPDATE command.

Alternatively since version 3.2, MongoDB also supports the following functions:

db.collectionName.updateOne(); /* updates a single document that matches a specified filter 
                                  (even if several documents match the filter) */

db.collectionName.updateMany(); /* updates all documents that matches a specified filter */

db.collectionName.replaceMany(); /* replaces  a single document that matches a specified filter             
                                    (even if several documents match the filter) */

Updating Department 40

To update department 40 to add some employees:

db.deptCollection.update({'deptno':40}, 
{$set: 
  {'employees': [   
    {
     empno: 8888,
     ename: 'MARY',
     job: 'LECTURER',
     mgr: 7566,
     hiredate: new Date(),
     sal: 4000
    },
    {
     empno: 9999,
     ename: 'SUSAN',
     job: 'LECTURER',
     mgr: 7566,
     hiredate: new Date(),
     sal: 3000
    } 
  ]}
}
)

Change the location to Wolverhampton:

db.deptCollection.update({'deptno':40}, 
 {$set:  {'loc': 'WOLVERHAMPTON'}})

Check the changes have been made:

db.deptCollection.find({"deptno":40}).pretty()

The salary should have been 3000 for both lecturers. There is an issue with the current design, in that the whole array has to be redefined. What happens if we try just the following:

db.deptCollection.update({'deptno':40}, 
 {$set: 
   {'employees': [   
     {
      empno: 8888,
      ename: 'MARY',
      job: 'LECTURER',
      mgr: 7566,
      hiredate: new Date(),
      sal: 3000
     } 
   ]}
 }
)

Check what changes have been made to Department 40. Is this what you expected?

Adding to the Employees Array

The Employees field is an array of employees and can be manipulated using [array-update] functions.

For example, to add a new employee to department 10, the addToSet operator can be used:

db.deptCollection.update ( { deptno: 10 }, { $addToSet: {employees: {
     empno: 5555,
     ename: 'SANJIT',
     job: 'LECTURER',
     mgr: 8888,
     hiredate: new Date(),
     sal: 3500 } }
 })

Removing an element from the Employees Array

Employees can be deleted using the $pull operator:

db.deptCollection.update ( { deptno: 40 }, 
 { $pull: {employees: { empno: 8888 } } }
)

The employees array will now be empty:

db.deptCollection.find({"deptno":40}).pretty()

Exercise 2.2

• 2.2.1 Update the name of department 40 to: COMPUTING
• 2.2.1 Update department 40 so both lecturers are still present

Next Step

Deleting a document.