Question 115760 in Mongodb Question posted in
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Is there any way of creating a unique index which allows empty values in mongodb?

I am trying to create a index with schema

{
   _id: "",
   name: ""
}

I want to make an index that supports names with unique values and permits adding data to databases when names have the value "" (empty string).

I tried using this:

db.collection.createIndex(
   {name: 1}, 
   {unique: true, partialFilterExpression: {name: {$type: "string"}}}
)
Tags:

2

Answers


  1. 0

    An empty string "" is still a string, so partialFilterExpression: {name: {$type: "string"}} will index this document.

    In principle, it would be this one:

    db.collection.createIndex(
   {name: 1}, 
   {unique: true, partialFilterExpression: {name: {$ne: ""}}}
)

    However, partialFilterExpression supports only these operators:

    • equality expressions (i.e. field: value or using the $eq operator),
    • $exists: true expression,
    • $gt, $gte, $lt, $lte expressions,
    • $type expressions,
    • $and operator,
    • $or operator,
    • $in operator

    Looks like, this is not possible. Only way would be to skip the attribute and use { partialFilterExpression: { name: { $exists: true } } }

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  2. 0

    You can use the string sort ordering to skip the empty string.

    Have the partial filter require that name be type string and greater than "":

    partialFilterExpression: {$and: [
                                  {name: {$type: "string"}},
                                  {name: {$gt: ""}}
                          ]}
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