How to change the type of a field

Question

I am trying to change the type of a field from within the mongo shell   I am doing this     db meta update      fields properties default      type   1          fields properties default      type   2        But it s not working

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db coll find   forEach function data        db coll update   id data  id    set  myfield parseInt data myfield

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Starting Mongo 4 2  db collection update   can accept an aggregation pipeline  finally allowing the update of a field based on its own value        a   45   b   x         a   53   b   y    db collection update      a      type  1            set    a     toString    a              multi  true          a   45   b   x         a   53   b   y       The first part   a      type  1     is the match query    It filters which documents to update  In this case  since we want to convert  a  to string when its value is a double  this matches elements for which  a  is of type 1  double    This table provides the codes representing the different possible types   The second part     set    a     toString    a         is the update aggregation pipeline    Note the squared brackets signifying that this update query uses an aggregation pipeline   set is a new aggregation operator  Mongo 4 2  which in this case modifies a field  This can be simply read as   set  the value of  a  to   a  converted   toString   What s really new here  is being able in Mongo 4 2 to reference the document itself when updating it  the new value for  a  is based on the existing value of   a   Also note   toString  which is a new aggregation operator introduced in Mongo 4 0   Don t forget   multi  true    otherwise only the first matching document will be updated      In case your cast isn t from double to string  you have the choice between different conversion operators introduced in Mongo 4 0 such as  toBool   toInt       And if there isn t a dedicated converter for your targeted type  you can replace    toString    a    with a  convert operation     convert    input    a   to  2     where the value for to can be found in this table   db collection update      a      type  1            set    a     convert    input    a   to  2               multi  true

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To convert a field of string type to date field  you would need to iterate the cursor returned by the find   method using the forEach   method  within the loop convert the field to a Date object and then update the field using the  set operator   Take advantage of using the Bulk API for bulk updates which offer better performance as you will be sending the operations to the server in batches of say 1000 which gives you a better performance as you are not sending every request to the server  just once in every 1000 requests     The following demonstrates this approach  the first example uses the Bulk API available in MongoDB versions  gt   2 6 and  lt  3 2  It updates all the documents in the collection by changing all the created at fields to date fields   var bulk   db collection initializeUnorderedBulkOp        counter   0   db collection find   created at      exists   true    type   2     forEach function  doc        var newDate   new Date doc created at       bulk find     id   doc  id    updateOne              set      created at   newDate               counter        if  counter   1000    0            bulk execute       Execute per 1000 operations and re-initialize every 1000 update statements         bulk   db collection initializeUnorderedBulkOp                Clean up remaining operations in queue if  counter   1000    0    bulk execute        The next example applies to the new MongoDB version 3 2 which has since deprecated the Bulk API and provided a newer set of apis using bulkWrite     var bulkOps        db collection find   created at      exists   true    type   2     forEach function  doc         var newDate   new Date doc created at       bulkOps push                                   updateOne                       filter       id   doc  id                                    update       set      created at   newDate                                                                  db collection bulkWrite bulkOps     ordered   true

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The only way to change the  type of the data is to perform an update on the data where the data has the correct type   In this case  it looks like you re trying to change the  type from 1  double  to 2  string    So simply load the document from the DB  perform the cast  new String x   and then save the document again   If you need to do this programmatically and entirely from the shell  you can use the find      forEach function x      syntax     In response to the second comment below  Change the field bad from a number to a string in collection foo   db foo find     bad       type   1       forEach  function  x         x bad   new String x bad      convert field to string   db foo save x

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demo change type of field mid from string to mongo objectId using mongoose    Post find      mid  1  id 1   exec function  err  doc                 doc map  item  key    gt                    Post findByIdAndUpdate   id item  id    set  mid  mongoose Types ObjectId item mid     exec  err res   gt                       if err  throw err                      reply res                                                     Mongo ObjectId is just another example of such styles as  Number  string  boolean that hope the answer will help someone else

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all answers so far use some version of forEach  iterating over all collection elements client-side   However  you could use MongoDB s server-side processing by using aggregate pipeline and  out stage as       the  out stage atomically replaces the existing collection with the   new results collection    example   db documents aggregate                           project                    id  1                 numberField     substr     numberField   0  -1                    otherField  1                 differentField  1                 anotherfield  1                 needolistAllFieldsHere  1                                                    out   documents

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To convert int32 to string in mongo without creating an array just add    to your number  -   db foo find     mynum       type   16       forEach  function  x         x mynum   x mynum          convert int32 to string   db foo save x

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You can easily convert the string data type to numerical data type  Don t forget to change collectionName  amp  FieldName  for ex   CollectionNmae   Users  amp  FieldName   Contactno    Try this query    db collectionName find   forEach  function  x    x FieldName   parseInt x FieldName   db collectionName save x

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Convert String field to Integer   db db-name find  field-name    exists  true    forEach function obj         obj field-name   new NumberInt obj field-name       db db-name save obj         Convert Integer field to String   db db-name find  field-name    exists  true    forEach function obj        obj field-name        obj field-name      db db-name save obj

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I use this script in mongodb console for string to float conversions     db documents find    fwtweaeeba      exists   true    forEach  function obj             obj fwtweaeeba   parseFloat  obj fwtweaeeba             db documents save obj             db documents find    versions 0 content fwtweaeeba      exists   true    forEach  function obj             obj versions 0  content fwtweaeeba   parseFloat  obj versions 0  content fwtweaeeba             db documents save obj         db documents find    versions 1 content fwtweaeeba      exists   true    forEach  function obj             obj versions 1  content fwtweaeeba   parseFloat  obj versions 1  content fwtweaeeba              db documents save obj         db documents find    versions 2 content fwtweaeeba      exists   true    forEach  function obj             obj versions 2  content fwtweaeeba   parseFloat  obj versions 2  content fwtweaeeba              db documents save obj          And this one in php     foreach  db- gt documents- gt find array  type    gt   chair    as  document        db- gt documents- gt update          array   id    gt   document  id            array                set    gt  array                   versions 0 content axdducvoxb    gt   float  document  versions   0   content    axdducvoxb                     versions 1 content axdducvoxb    gt   float  document  versions   1   content    axdducvoxb                     versions 2 content axdducvoxb    gt   float  document  versions   2   content    axdducvoxb                     axdducvoxb    gt   float  document  axdducvoxb                                    array   multi    gt  true

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What really helped me to change the type of the object in MondoDB was just this simple line  perhaps mentioned before here      db Users find  age    exists  true    forEach function obj        obj age   new NumberInt obj age       db Users save obj         Users are my collection and age is the object which had a string instead of an integer  int32

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I need to change datatype of multiple fields in the collection  so I used the following to make multiple data type changes in the collection of documents  Answer to an old question but may be helpful for others   db mycoll find   forEach function obj          if  obj hasOwnProperty  phone              obj phone        obj phone      int or longint to string            if  obj hasOwnProperty  field-name           obj field-name   new NumberInt obj field-name     string to integer            if  obj hasOwnProperty  cdate              obj cdate   new ISODate obj cdate     string to Date            db mycoll save obj

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For string to int conversion    db my collection find   forEach  function obj        obj my value  new NumberInt obj my value       db my collection save obj         For string to double conversion        obj my value  parseInt obj my value  10     For float       obj my value  parseFloat obj my value

[mongodb] How to change the type of a field?

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