Specify a Query

Overview

In this guide, you can learn how to specify a query by using the Scala driver.

You can refine the set of documents that a query returns by creating a query filter. A query filter is an expression that specifies the search criteria that MongoDB uses to match documents in a read or write operation.

You can use query operators to express more complex matching criteria in a query filter. The Scala driver includes a Filters class that provides helper methods for applying query operators.

val uri: String = "<connection string>"
val client: MongoClient = MongoClient(uri)
val database: MongoDatabase = client.getDatabase("db")
val collection: MongoCollection[Document] = database.getCollection("fruits")
// Inserts documents representing fruits
val fruits: Seq[Document] = Seq(
    Document("_id" -> 1, "name" -> "apples", "qty" -> 5, "rating" -> 3, "color" -> "red", "type" -> Seq("fuji", "honeycrisp")),
    Document("_id" -> 2, "name" -> "bananas", "qty" -> 7, "rating" -> 4, "color" -> "yellow", "type" -> Seq("cavendish")),
    Document("_id" -> 3, "name" -> "oranges", "qty" -> 6, "rating" -> 2, "type" -> Seq("naval", "mandarin")),
    Document("_id" -> 4, "name" -> "pineapples", "qty" -> 3, "rating" -> 5, "color" -> "yellow")
)
val result = collection.insertMany(fruits)
                       .subscribe((result: InsertManyResult) => println(result))

Exact Match

Literal value queries return documents that have an exact match to your query filter.

The following example specifies a query filter as a parameter to the find() method. The code returns all documents in which the value of the color field is "yellow":

val filter = equal("color", "yellow")
collection.find(filter).subscribe((doc: Document) => println(doc.toJson()),
                            (e: Throwable) => println(s"There was an error: $e"))

{"_id": 2, "name": "bananas", "qty": 7, "rating": 4, "color": "yellow", "type": ["cavendish"]}
{"_id": 4, "name": "pineapples", "qty": 3, "rating": 5, "color": "yellow"}

collection.find()

Comparison Operators

Comparison operators evaluate a document field value against a specified value in your query filter. The following list defines common comparison operators and their corresponding Filters helper methods:

The following example passes a query filter to the find() method and uses the gt() method to apply the $gt comparison operator. The code returns all documents in which the value of the rating field is greater than 2:

val filter = gt("rating", 2)
collection.find(filter).subscribe((doc: Document) => println(doc.toJson()),
                            (e: Throwable) => println(s"There was an error: $e"))

{"_id": 1, "name": "apples", "qty": 5, "rating": 3, "color": "red", "type": ["fuji", "honeycrisp"]}
{"_id": 2, "name": "bananas", "qty": 7, "rating": 4, "color": "yellow", "type": ["cavendish"]}
{"_id": 4, "name": "pineapples", "qty": 3, "rating": 5, "color": "yellow"}

Logical Operators

Logical operators match documents by using logic applied to the results of two or more sets of expressions. The following table describes each logical operator and its corresponding Filters helper method:

The following example passes a query filter to the find() method and uses the or() method to apply the $or logical operator. The code returns all documents in which the qty field value is greater than 5 or the color field value is "yellow":

val filter = or(gt("qty", 5), equal("color", "yellow"))
collection.find(filter).subscribe((doc: Document) => println(doc.toJson()),
                            (e: Throwable) => println(s"There was an error: $e"))

{"_id": 2, "name": "bananas", "qty": 7, "rating": 4, "color": "yellow", "type": ["cavendish"]}
{"_id": 3, "name": "oranges", "qty": 6, "rating": 2, "type": ["naval", "mandarin"]}
{"_id": 4, "name": "pineapples", "qty": 3, "rating": 5, "color": "yellow"}

Array Operators

Array operators match documents based on the value or quantity of elements in an array field. The following table describes each array operator and its corresponding Filters helper method:

The following example passes a query filter to the find() method and uses the size() method to apply the $size array operator. The code returns all documents in which the type array field contains 2 elements:

val filter = size("type", 2)
collection.find(filter).subscribe((doc: Document) => println(doc.toJson()),
                            (e: Throwable) => println(s"There was an error: $e"))

{"_id": 1, "name": "apples", "qty": 5, "rating": 3, "color": "red", "type": ["fuji", "honeycrisp"]}
{"_id": 3, "name": "oranges", "qty": 6, "rating": 2, "type": ["naval", "mandarin"]}

Element Operators

Element operators query data based on the presence or type of a field. The following table describes each element operator and its corresponding Filters helper method:

The following example passes a query filter to the find() method and uses the exists() method to apply the $exists element operator. The code returns all documents that have a color field:

val filter = exists("color")
collection.find(filter).subscribe((doc: Document) => println(doc.toJson()),
                            (e: Throwable) => println(s"There was an error: $e"))

{"_id": 1, "name": "apples", "qty": 5, "rating": 3, "color": "red", "type": ["fuji", "honeycrisp"]}
{"_id": 2, "name": "bananas", "qty": 7, "rating": 4, "color": "yellow", "type": ["cavendish"]}
{"_id": 4, "name": "pineapples", "qty": 3, "rating": 5, "color": "yellow"}

Evaluation Operators

Evaluation operators return data based on evaluations of either individual fields or the entire collection's documents. The following table describes common element operators and their corresponding Filters helper methods:

The following example passes a query filter to the find() method and uses the regex() method to apply the $regex evaluation operator. The code uses a regular expression to return all documents in which the name field value has at least two consecutive 'p' characters:

val filter = regex("name", "p{2,}")
collection.find(filter).subscribe((doc: Document) => println(doc.toJson()),
                            (e: Throwable) => println(s"There was an error: $e"))

{"_id": 1, "name": "apples", "qty": 5, "rating": 3, "color": "red", "type": ["fuji", "honeycrisp"]}
{"_id": 4, "name": "pineapples", "qty": 3, "rating": 5, "color": "yellow"}

Additional Information

To learn more about querying documents, see the Query Documents guide in the MongoDB Server manual.

To learn more about retrieving documents with the Scala driver, see the Retrieve Data guide.