Likely, it's because you have an index that requires a unique value for one of the fields as shown below:
> db.servers.remove()
> db.servers.ensureIndex({"name": 1}, { unique: 1})
> db.servers.insert({"_id": "1.2.3"})
> db.servers.insert({"_id": "1.2.4"})
E11000 duplicate key error index: test.servers.$name_1 dup key: { : null }
You can see your indexes using getIndexes()
on the collection:
> db.servers.getIndexes()
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"ns" : "test.servers",
"name" : "_id_"
},
{
"v" : 1,
"key" : {
"name" : 1
},
"unique" : true,
"ns" : "test.servers",
"name" : "name_1"
}
]
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