mongodb populate flat file results?

Question

I am trying to remove old files from the file system
The file list is maintained in mongoDb collection like so:

{
    "_id" : ObjectId("59a39215953f77968789d692"),
    "className" : "com.xerox.model.ModuleDocument",
    "documentId" : "0000001643",
    "documentDate" : ISODate("2017-05-11T04:00:00.000Z"),
    "documentType" : "PRINTER_VALIDATION_2017",
    "module" : "PRINTERS",
    "printerId" : "1002563",
    "origFileName" : "0000001643.JPG",
    "isDeleted" : true
}

But when I query the DB using the mongo shell

 db.getCollection('xerox_documents').find({"isDeleted":true})

The result is displayed as JSON, Is it possible to get the results in flat text format? The desired output is something like:

DEL c:\DOCS\PRINTERS\PRINTER_VALIDATION_2017\0000001643.JPG  
DEL c:\DOCS\PRINTERS\PRINTER_VALIDATION_2017\0000001643.JPG

can you please explain more... which field you want to be in text format? — Ashh, Jul 03 '18 at 19:01
just loop over the results with a `forEach` and use `print` function to format the string. — Marco Luzzara, Jul 03 '18 at 19:05

score 2 · Answer 1 · answered Jul 03 '18 at 19:09

You need to use $concat to concatenate any field in the collection

db.getCollection('xerox_documents').aggregate([
  { "$match": { "isDeleted": true }},
  { "$project": {
    "origFileName": {
      "$concat": [ "c:\DOCS\PRINTERS\PRINTER_VALIDATION_2017\", "$origFileName" ]
    }
  }}
])

Marco Luzzara · Accepted Answer · 2018-07-03T20:43:11.760

Do not forget that mongodb script are closely related to js script.

db.getCollection('xerox_documents').find({"isDeleted": true}).forEach(elem => {
    print(`DEL c:\\DOCS\\${elem.module}\\${elem.documentType}\\${elem.origFileName}`);
});

You can use print() to format your results as raw text. The find() function returns a cursor, which is a pointer to the result query. Think of it as an iterator on which you can call the forEach function, that has the same signature as the Array.forEach in js.

Looping over a Cursor can be made in other 2 ways:

Manually calling next() until hasNext() is true. It's a typical scheme for an Iterable.
Using Cursor.toArray() to generate an array that stores all the results into an array. Watch out because they are loaded into RAM.

The lambda function I have put as argument in forEach is interpreted as a full-fledged js function.

mongodb populate flat file results?

2 Answers2