how to lower case the value of unique:true keys in mongodb? - mongodb

Question

I have created a mongodb and by mistake have entered duplicate values in the form of capital and small case letters.
I have made the index unique. MongoDB is case sensitive and hence, considered the capital letter and small letter as different values.
Now my problem is the database have got around 32 GB. and I came across this issue. Kindly help me.
Here is the sample:
db.tt.createIndex({'email':1},{unique:true})
> db.tt.find().pretty()
{
"_id" : ObjectId("591d706c0ef9acde11d7af66"),
"email" : "g#gmail.com",
"src" : [
{
"acc" : "ln"
},
{
"acc" : "drb"
}
]
}
{
"_id" : ObjectId("591d70740ef9acde11d7af68"),
"email" : "G#gmail.com",
"src" : [
{
"acc" : "ln"
},
{
"acc" : "drb"
},
{
"acc" : "dd"
}
]
}
How I can make the email as lowercase and assign the src values to the original one. Kindly help me.

Answer 1

you can achive this using $toLower aggregation operator like this :
db.tt.aggregate([
{
$project:{
email:{
$toLower:"$email"
},
src:1
}
},
{
$unwind:"$src"
},
{
$group:{
_id:"$email",
src:{
$addToSet:"$src"
}
}
},
{
$project:{
_id:0,
email:"$_id",
src:1
}
},
{
$out:"anotherCollection"
}
])
$addToSet allow to keep oly one distinct occurence of src items
this will write this document to a new collection named anotherCollection:
{ "email" : "g#gmail.com", "src" : [ { "acc" : "dd" }, { "acc" : "drb" }, { "acc" : "ln" } ] }
Note that with $out, you can averwrite directly your tt collection, however before doing this make sure to understand what your doing because all previous data will be lost

Answer 2

The most efficient way I can think of to merge the data is run an aggregation and loop the result to write back to the collection in bulk operations:
var ops = [];
db.tt.aggregate([
{ "$unwind": "$src" },
{ "$group": {
"_id": { "$toLower": "$email" },
"src": { "$addToSet": "$src" },
"ids": { "$addToSet": "$_id" }
}}
]).forEach(doc => {
var id = doc.ids.shift();
ops = [
...ops,
{
"deleteMany": {
"filter": { "_id": { "$in": doc.ids } }
}
},
{
"updateOne": {
"filter": { "_id": id },
"update": {
"$set": { "email": doc._id },
"$addToSet": { "src": { "$each": doc.src } }
}
}
},
];
if ( ops.length >= 500 ) {
db.tt.bulkWrite(ops);
ops = [];
}
});
if ( ops.length > 0 )
db.tt.bulkWrite(ops);
In steps, that's $unwind the array items so they can be merged via $addToSet, under a $group on using $toLower on the email value. You also want to keep the set of unique source document ids.
In the loop you shift the first _id value off of doc.ids and update that document with the lowercase email and the revised "src" set. Using $addToSet here makes the operation write safe with any other updates that might occur to the document.
Then the other operation in the loop deletes the other documents that shared the same converted case email, so there are no duplicates. Actually do that one first. The default "ordered" operations make sure this is fine.
And do it in the shell, since it's a one-off operation and is really just as simple as listing as shown.