{"id":28229,"date":"2023-09-27T09:56:22","date_gmt":"2023-09-27T07:56:22","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/?p=28229"},"modified":"2023-09-27T09:56:26","modified_gmt":"2023-09-27T07:56:26","slug":"mongodb-identify-a-field-type","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/mongodb-identify-a-field-type\/","title":{"rendered":"MongoDB: Identify a field type"},"content":{"rendered":"\n

Introduction<\/h2>\n\n\n\n

Whereas I wanted to perform a quick demo to show some MongoDB useful command to mass<\/p>\n\n\n\n

update some fields (Increment),I had a MongoDB error: \u201cCannot increment with a non-numeric argument\u201d<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

I guess the message is explicit:<\/p>\n\n\n\n

I can\u2019t update this field as it is not a numeric field<\/p>\n\n\n\n

Identify the field type:<\/h2>\n\n\n\n

As I have created my document with basic commands without specifying each field type, the fields are set by default (undefined<\/strong> )<\/p>\n\n\n\n

How to know the type of your field?<\/h2>\n\n\n\n

For my example I have this list of players, their name, and also their number<\/strong> of goals.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

When I wanted to increment the “goals” field by 10 it displayed the famous issue.<\/p>\n\n\n\n

Let’s check the goals field type:<\/p>\n\n\n\n

For that we will use the below command:<\/p>\n\n\n\n

typeof <\/strong>db.collection.findOne().field_name<\/strong><\/code><\/pre>\n\n\n\n
selecao_cracks> typeof db.selecao_cracks.findOne().Lastname<\/code><\/pre>\n\n\n\n
\"\"<\/figure>\n\n\n\n
Here we see that Lastname <\/strong>field is undefined<\/p>\n\n\n\n
If we take a look we see that Nickname field is a string type (I made some tests before) <\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
The $TYPE operator:<\/h2>\n\n\n\n
The $type<\/code><\/a> operator accepts string aliases for the BSON types in addition to the numbers corresponding to the BSON types<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
Update the type of the field<\/h2>\n\n\n\n
Use the $set<\/strong> operator and the $toInt<\/strong> operator to update the field ( In fact in that case the $set<\/strong> operator will replace the field and its type, later we will see that we can use another operator name $convert <\/strong>)<\/p>\n\n\n\n
selecao_cracks> db.selecao_cracks.updateMany( {}, [{ $set<\/strong> : { \"goals\":{$toInt<\/strong>:\"$goals\"}}} ]);<\/code><\/pre>\n\n\n\n
\"\"<\/figure>\n\n\n\n