Find and Replace Strings in Documents Efficiently

Question

I have the following query, to find   tags in a name field and replace them with an empty space - to get rid of them.
Name strings can have 1 to many   tags e.g.

AA aa
AA  aa
AA   aa
AA    aa
AA AA aaaaaaaa

... like that.

  db.tests.find({'name':/.* .*/}).forEach(function(test){
      test.name = test.name.replace(" ","");
      db.tests.save(test);
   });

   db.tests.find({'name':/.*  .*/}).forEach(function(test){
      test.name = test.name.replace("  ","");
      db.tests.save(test);
   });

  db.tests.find({'name':/.*   .*/}).forEach(function(test){
      test.name = test.name.replace("   ","");
      db.tests.save(test);
   });

Other than repeating the same query pattern, is there a better solution to handle this scenario, in terms of less duplication and higher performance?

Answer 1

Nowadays,

• starting Mongo 4.2, db.collection.updateMany (alias of db.collection.update) can accept an aggregation pipeline, finally allowing the update of a field based on its own value.
• starting Mongo 4.4, the new aggregation operator $replaceAll makes it very easy to replace parts of a string.

// { "name" : "AA aa" }
// { "name" : "AA  aa" }
// { "name" : "AA AA aaaaaaaa" }
db.collection.updateMany(
  { name: { $regex: /\&nbsp\;/ } },
  [{
    $set: { name: {
      $replaceAll: { input: "$name", find: " ", replacement: "" }
    }}
  }]
)
// { "name" : "AAaa" }
// { "name" : "AAaa" }
// { "name" : "AAAAaaaaaaaa" }

• The first part ({ name: { $regex: /\&nbsp\;/ } }) is the match query, filtering which documents to update (the ones containing " ")
• The second part ($set: { name: {...) is the update aggregation pipeline (note the squared brackets signifying the use of an aggregation pipeline):
  • $set is a new aggregation operator (Mongo 4.2) which in this case replaces the value of a field.
  • The new value is computed with the new $replaceAll operator. Note how name is modified directly based on the its own value ($name).

Answer 2

As   does not appear as a string in MongoDB search, hence instead of a string, I have used its UNICODE u00a0 as shown below:

db.tests.find({}).forEach(function (x) {
    x.name = x.name.replace(/\u00a0/g, ' ');

    db.tests.save(x);
});

Here, I am replacing   in name data field with white space