MongoDB text index and text search

Question

I have a MongoDB collection db.articles,it has 2 keys ,"title" and "abstract".I want to do text search on these two keys.For example, the search text is "physics",and I want all the documents whose "title" or "abstract" contains keyword "physics" is returned.But how to create the text index to meet my command is really confusing me:

Should I create two separate text indexes for both of them like this:

db.articles.ensureIndex({title:"text"})
db.articles.ensureIndex({abstract:"text"})

or

should I create a index in a single command and give the equal weight:

db.articles.ensureIndex(
                     {
                       title: "text",
                       abstract: "text",
                     },
                     {
                       weights: {
                                  title: 1,
                                  abstract:1,
                                },
                       name: "TextIndex"
                     }
                   )

I am already get used to the operation find(),whose query granularity is key,that is ,you should indicate the key you want to query on.But for text index, it seems like a document granularity,you cannot indicate the key you want to query on , instead ,you can only indicate the document name.So , what can I do if I want to do text search on a special key?

Answer 1

So, no need to test as it turns out, I just remembered the key deciding limitations. You can only create one text index on a collection (reference here), so you have no real choice. Additionally, MongoDB can only use one index at a time to satisfy a query (until index intersection is introduced in 2.6).

Hence, the only workable option is to create the compound index as you outlined, on both fields as a single index:

db.articles.ensureIndex(
                     {
                       title: "text",
                       abstract: "text",
                     },
                     {
                       weights: {
                                  title: 1,
                                  abstract:1,
                                },
                       name: "TextIndex"
                     }
                   )

The same remains true for 3 or 4 fields, you would first have to drop the existing index, then create the new index and include 3/4/other.

Answer 2

I want to do text search on these two keys.For example, the search text is "physics",and I want all the documents whose "title" or "abstract" contains keyword "physics" is returned.

To perform text search, MongoDB uses a text index and the $text operator.

MongoDB provides text indexes to support text search queries on string content. text indexes can include any field whose value is a string or an array of string elements.

To perform text search queries, you must have a text index on your collection. A collection can only have one text search index, but that index can cover multiple fields.

As per MongoDB BOL db.collection.ensureIndex() Deprecated since version 3.0.0: db.collection.ensureIndex() is now an alias for db.collection.createIndex().

The db.collection.ensureIndex() Creates an index on the specified field if the index does not already exist.

Note: Use db.collection.createIndex() rather than db.collection.ensureIndex() to create new indexes.

Should I create two separate text indexes for both of them like this:

db.articles.ensureIndex({title:"text"})
db.articles.ensureIndex({abstract:"text"})

For example you can run the following in a mongo shell to allow text search over the name and comments fields:

> db.articles.createIndex( { title: "text", comments: "text" } )
{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 1,
        "numIndexesAfter" : 2,
        "ok" : 1
}

To make sure you have created the index on not through db.collection.getIndexes() Which returns an array that holds a list of documents that identify and describe the existing indexes on the collection. You must call db.collection.getIndexes() on a collection.

> db.articles.getIndexes()
[
        {
                "v" : 2,
                "key" : {
                        "_id" : 1
                },
                "name" : "_id_",
                "ns" : "test.articles"
        },
        {
                "v" : 2,
                "key" : {
                        "_fts" : "text",
                        "_ftsx" : 1
                },
                "name" : "title_text_comments_text",
                "ns" : "test.articles",
                "weights" : {
                        "comments" : 1,
                        "title" : 1
                },
                "default_language" : "english",
                "language_override" : "language",
                "textIndexVersion" : 3
        }
]
>

Here the index name "title_text_comments_text" has created for both field.

So, No need to create again text index on specified both field.

should I create a index in a single command and give the equal weight:

db.articles.createIndex(
   {
     title: "text",
     comments: "text"
   }
 )

My Answer is Yes .

Let's after creation of multiple fields for the text index ( like mention in your second scenario).

> db.articles.createIndex(
...    {
...      title: "text",
...      comments: "text"
...    }
...  )
{
        "createdCollectionAutomatically" : false,
        "numIndexesBefore" : 2,
        "numIndexesAfter" : 2,
        "note" : "all indexes already exist",
        "ok" : 1
}
>

To verify from the db.collection.getIndexes() method

> db.articles.getIndexes()
[
        {
                "v" : 2,
                "key" : {
                        "_id" : 1
                },
                "name" : "_id_",
                "ns" : "test.articles"
        },
        {
                "v" : 2,
                "key" : {
                        "_fts" : "text",
                        "_ftsx" : 1
                },
                "name" : "title_text_comments_text",
                "ns" : "test.articles",
                "weights" : {
                        "comments" : 1,
                        "title" : 1
                },
                "default_language" : "english",
                "language_override" : "language",
                "textIndexVersion" : 3
        }
]
>

After execution of text index in mongo shell, In the above statement we can see there come short note like "note" : "all indexes already exist". So, we can say that both scenario the creation of text index is same.

Most Important Note : A collection can have at most one text index.

In the above example the database name is test and collection name is articles (Because as OP has used in their Code).