Mongo unique index case insensitive

Prior of MongoDB version 3.4 we were unable to create index with case insensitive.

In version 3.4 has collation option that allows users to specify language-specific rules for string comparison, such as rules for lettercase and accent marks.

The collation option has the following syntax:

collation: {
   locale: <string>,
   caseLevel: <boolean>,
   caseFirst: <string>,
   strength: <int>,
   numericOrdering: <boolean>,
   alternate: <string>,
   maxVariable: <string>,
   backwards: <boolean>
}

where the locale field is mandatory; all other fields are optional.

To create index with case insensitive we need to use mandatory field locale and strength field for string comparison level. strength allows value rage 1 – 5. read more about collation

The strength attribute determines whether accents or case are taken into account when collating or matching text

Example:

if strength=1 then role = Role = rôle

if strength=2 then role = Role < rôle

if strength=3 then role < Role < rôle

Comparison level doc

So we need to use strength=2 to create index. like:

db.collectionName.createIndex(
  { name: 1, formula: 1, type: 1 },
  { 
    name: "fertilizer_idx",
    collation: {locale: "en", strength: 2},
    unique: true
  }
)

N.B: collation option is not available for text indexes.