Understanding Database Update Operators

When performing updates on objects in MongoDB, you need to specify exactly what fields need to be changed and how they need to be changed. Unlike in SQL, where you create long query strings to define an update, in MongoDB you can implement an update object with operators that define exactly how to change the data in the documents.

You can include as many operators in the update object as you need. The format of the update object is shown below:

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{
  <operator>: {<field_operation>, <field_operation>, . . .},
  <operator>: {<field_operation>, <field_operation>, . . .}
  . . .
}

For example, consider the following object:

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{
  name: "myName",
  countA: 0,
  countB: 0,
  days: ["Monday", "Wednesday"],
  scores: [ {id:"test1", score:94}, {id:"test2", score:85}, {id:"test3", score:97}]
}

Use the following update object if you want to increment the countA field by 5, increment countB by 1, set name to "New Name", add Friday to the days array, and sort the scores array by the score field:

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{
  $inc:{countA:5, countB:1},
  $set:{name:"New Name"},
  $push{days:"Friday},
  $sort:{score:1}
}

Table 14.2 lists the operators you can use in the update object to update documents.

Table 14.2 Operators you can specify in the update object when performing update operations