Language Analyzers

Built-In Language Analyzer Example

The following example index definition specifies an index on the subject.fr field using the french analyzer:

{
  "mappings": {
    "fields": {
      "subject": {
        "fields": {
          "fr": {
            "analyzer": "lucene.french",
            "type": "string"
          }
        },
        "type": "document"
      }
    }
  }
}

The following query searches for the string pour in the subject.fr field:

db.cars.aggregate([
  {
    $search: {
      "text": {
        "query": "pour",
        "path": "subject.fr"
      }
    }
  },
  {
    $project: {
      "_id": 0,
      "subject.fr": 1
    }
  }
])

The previous query returns no results when using the french analyzer, because pour is a built-in stop word. Using the standard analyzer, the same query would return both documents.

The following query searches for the string carburant in the subject.fr field:

db.cars.aggregate([
  {
    $search: {
      "text": {
        "query": "carburant",
        "path": "subject.fr"
      }
    }
  },
  {
    $project: {
      "_id": 0,
      "subject.fr": 1
    }
  }
])

{ subject: { fr: "Le meilleur moment pour le faire c'est immédiatement après que vous aurez fait le plein de carburant." } }

MongoDB Search returns a document with _id: 1 in the results because the query matched a token that the lucene.french analyzer created for the document. The lucene.french analyzer creates the following tokens for the subject.fr field in document with _id: 1:

Custom Language Analyzer Example

You can also create indexes for unsupported languages by creating a custom analyzer with the icuFolding and stopword token filters.

The following example index definition specifies an index on the subject.he field using a custom analyzer called myHebrewAnalyzer to analyze and create tokens for Hebrew text:

{
  "analyzer": "lucene.standard",
  "mappings": {
    "dynamic": false,
    "fields": {
      "subject": {
        "fields": {
          "he": {
            "analyzer": "myHebrewAnalyzer",
            "type": "string"
          }
        },
        "type": "document"
      }
    }
  },
  "analyzers": [
    {
      "charFilters": [],
      "name": "myHebrewAnalyzer",
      "tokenFilters": [
        {
          "type": "icuFolding"
        },
        {
          "tokens": [
            "אן",
            "שלנו",
            "זה",
            "אל"
          ],
          "type": "stopword"
        }
      ],
      "tokenizer": {
        "type": "standard"
      }
    }
  ]
}

The following query searches for the string המכוניות in the subject.he field:

db.cars.aggregate([
  {
    $search: {
      "text": {
        "query": "המכוניות",
        "path": "subject.he"
      }
    }
  },
  {
    $project: {
      "_id": 0,
      "subject.he": 1
    }
  }
])

{ subject: { he: 'עדיף לצייד את המכוניות שלנו כדי להבין את הגורמים לתאונה.' } }

MongoDB Search returns a document with _id: 1 in the results because the query matched a token that the myHebrewAnalyzer analyzer created for document. The myHebrewAnalyzer analyzer creates the following tokens for the subject.he field in document with _id: 1:

Multilingual Search Example

You can also create an index that uses multiple language analyzers to perform a multilingual search.

The following example index definition specifies an index with dynamic mapping on the sample_mflix.movies collection. The definition applies the lucene.italian language analyzer to index the fullplot field, and uses the multi option to specify lucene.english as an alternate language analyzer. MongoDB Search uses the default lucene.english language analyzer for all other fields that it dynamically indexes in the movies collection.

{
  "analyzer": "lucene.standard",
  "mappings": {
    "dynamic": true,
    "fields": {
      "fullplot": {
        "type": "string",
        "analyzer": "lucene.italian",
        "multi": {
          "fullplot_english": {
            "type": "string",
            "analyzer": "lucene.english",
          }
        }
      }
   }
  }
}

The following MongoDB Search query uses the following compound operator clauses to query the collection:

• must clause searches for movie plots in English and Italian that contain the term Bella using the text operator

• mustNot clause excludes movies released between the years 1984 to 2016 using the range operator

• should clause specifies preference for the Comedy genre using the text operator

[
  {
    $search: {
      "index": "multilingual-tutorial",
      "compound": {
        "must": [{
          "text": {
            "query": "Bella",
            "path": { "value": "fullplot", "multi": "fullplot_english" }
          }
        }],
        "mustNot": [{
          "range": {
            "path": "released",
            "gt": ISODate("1984-01-01T00:00:00.000Z"),
            "lt": ISODate("2016-01-01T00:00:00.000Z")
          }
        }],
        "should": [{
          "text": {
            "query": "Comedy",
            "path": "genres"
          }
        }]
      }
    }
  }
]

SCORE: 3.909510850906372  _id: "573a1397f29313caabce8bad"
  plot: "He is a revenge-obssessed stevedore whose sister was brutally raped an…"
  genres:
    0: "Drama"
  runtime: 137
  fullplot: "In Marseilles, a woman commits suicide after she is raped in an alley.…"
  released: 1983-05-18T00:00:00.000+00:00
SCORE: 3.4253346920013428  _id: "573a1396f29313caabce5735"
  plot: "Giovanna e' una bella ragazza, ma ha qualche problema con gli uomini: …"
  genres:
    0: "Comedy"
  runtime: 100
  fullplot: "Giovanna e' una bella ragazza, ma ha qualche problema con gli uomini: …"
  released: 1974-11-15T00:00:00.000+00:00
SCORE: 3.363344430923462  _id: "573a1395f29313caabce13cf"
  plot: "Gerardo è un attore o almeno cerca di esserlo, ma il pubblico non è de…"
  genres:
    0: "Comedy"
  runtime: 95
  fullplot: "Gerardo è un attore o almeno cerca di esserlo, ma il pubblico non è de…"
  released: 1960-02-10T00:00:00.000+00:00
SCORE: 1.9502882957458496  _id: "573a1396f29313caabce5299"
  plot: "Dr Tremayne is an enigmatic Psychiatrist running a
  Futuristic asylum h…"
  genres:
    0: "Horror"
  runtime: 90
  fullplot: "Dr Tremayne is an enigmatic Psychiatrist running a Futuristic asylum h…"
  released: 1973-10-31T00:00:00.000+00:00