exception: can't convert from BSON type EOO to Date

Question

I am getting an issue for running the following aggregate query:

db.snippets.aggregate([ { \'$project\': { month: { \'$month\': \'$created_at\' }} } ])


        

Answer 1

I had the same problem, I figured that the date field is missing for some of the documents causing the conversion to fail. I just added a match clause to filter these out. But ofcourse i am investigating on my app side why they are not being populated.

db.snippets.aggregate([
  {
    '$match': {
      'created_at': {
        "$exists": true
      }
    }
  },
  {
    '$project': {
      month: {
        '$month': '$created_at'
      }
    }
  }
])

Answer 2

This error can also appear if you have incorrectly named your properties in your aggregation relative to what they are in your database.

For example my code was

$group: {
        _id: {$week: "$projects.timeStamp"},
        total: { $sum: "$projects.hours"  }
    }

But I hadn't camelcased timestamp in my database so simply modifying to projects.timestamp fixed it.

Answer 3

I had a similar problem, and solved it checking if the date existed.

db.users.aggregate([
{$project:{day:  { $cond: ["$bd", { $dayOfMonth: "$bd" }, -1] },
           month:  { $cond: ["$bd", { $month: "$bd" }, -1] },
           year:  { $cond: ["$bd", { $year: "$bd" }, -1] }
           }},
{$match:{"month":1, "day":15}}
])

My date field is bd and with that match I'm getting all users that have their birthday on January 15th.

Answer 4

In some situations, some documents are supposed to have empty Date fields. In those cases, you could try this (using your example):

db.snippets.aggregate([ { '$project': { month:  
 { $cond: [{ $ifNull: ['$created_at', 0] }, { $month: '$created_at' }, -1] }} } ])

In this example, we would get -1 in the cases whenever no field '$created_at' is found. For all the other cases, we would get the Date month.

Answer 5

try this one, its help for me above problem.

db.snippets.aggregate([{
'$project': {
    month: { $substr: ["$created_at", 5, 2] }
}
 }]);

above code get month wise

data is entered into the database in ISO format which can then be easily worked with.

Answer 6

You likely have one or more docs with a created_at value that's not a BSON Date and you'll need to fix that by converting those values to Date or removing them.

You can find those docs with a $not query that uses the $type operator like:

db.snippets.find({created_at: {$not: {$type: 9}}})

If the created_at values are date strings, you can find the docs that need updating and then update them in the shell using code like:

db.snippets.find({created_at: {$not: {$type: 9}}}).forEach(function(doc) {
    // Convert created_at to a Date 
    doc.created_at = new Date(doc.created_at);
    db.snippets.save(doc);
})