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Criteria

Adds a Criteria DSL for creating ReactiveMongo queries

Overview

Original Query Syntax

The reactivemongo.api.collections.GenericCollection type provides the find method used to find documents matching a criteria. It is this interaction which the DSL targets. Originally, providing a selector to find had an interaction similar to:

  val cursor = collection.find(BSONDocument("firstName" -> "Jack")).cursor[BSONDocument]

This is, of course, still supported as the DSL does not preclude this usage.

Criteria DSL

What the DSL does provide is the ablity to formulate queries thusly:

  // Using an Untyped.criteria
  {
  import Untyped._

  // The MongoDB properties referenced are not enforced by the compiler
  // to belong to any particular type.  This is what is meant by "Untyped".
  val adhoc = criteria.firstName === "Jack" && criteria.age >= 18;
  val cursor = collection.find(adhoc).cursor[BSONDocument];
  }

Another form which achieves the same result is to use one of the where methods available:

  // Using one of the Untyped.where overloads
  {
  import Untyped._

  val cursor = collection.find(
    where (_.firstName === "Jack" && _.age >= 18)
	).cursor[BSONDocument];
  }

There are overloads for between 1 and 22 place holders using the where method. Should more than 22 be needed, then the 1 argument version should be used with a named parameter. This allows an infinite number of property constraints to be specified.

For situations where the MongoDB document structure is well known and a developer wishes enforce property existence, the Typed Criteria can be used:

  {
  // Using a Typed criteria which restricts properties to the
  // given type.
  import Typed._

  case class ExampleDocument (aProperty : String, another : Int)

  val byKnownProperties = criteria[ExampleDocument].aProperty =~ "^[A-Z]\\w+" &&
    criteria[ExampleDocument].another > 0;
  val cursor = collection.find(byKnownProperties).cursor[BSONDocument];
  }

Note that Typed and Untyped serve different needs. When the structure of a document collection is both known ''and'' identified as static, Typed makes sense to employ. However, Untyped is compelling when document structure can vary within a collection. These are considerations which can easily vary between projects and even within different modules of one project.

Roadmap

This section details the functionality either currently or planned to be supported by ReactiveMongo-Criteria.

  • Ability to formulate queries without requiring knowledge of document structure. COMPLETE
  • Ability to ''type check'' query constraints by specifying a Scala type. IN PROGRESS
  • Define and add support for an EDSL specific to projections. TBD

Operators

When using the Criteria DSL, the fact that the operators adhere to the expectations of both programmers and Scala precedences, most uses will "just work." For example, explicitly defining grouping is done with parentheses, just as you would do with any other bit of Scala code.

For the purposes of the operator API reference, assume the following code is in scope:

import reactivemongo.extensions.dsl.criteria.Untyped._

Comparison Operators

With the majority of comparison operators, keep in mind that the definition of their ordering is dependent on the type involved. For example, strings will use lexigraphical ordering whereas numbers use natural ordering.

  • ===, @== Matches properties based on value equality.
criteria.aProperty === "value"
criteria.aProperty @== "value"
  • <>, =/=, !== Matches properties which do not have the given value.
criteria.aProperty <> "value"
criteria.aProperty =/= "value"
criteria.aProperty !== "value"
  • < Matches properties which compare "less than" a given value.
criteria.aNumber < 99
  • <= Matches properties which compare "less than or equal to" a given value.
criteria.aNumber <= 99
  • > Matches properties which compare "greater than" a given value.
criteria.aProperty > "Alice"
  • >= Matches properties which compare "greater than or equal to" a given value.
criteria.aNumber >= 100

Existence Operators

  • exists Matches any document which has the specified field.
criteria.aProperty.exists
  • in Matches properties which are arrays and have one of the given values.
criteria.anArray.in (1, 2, 3, 4, 5)
  • all Matches array properties which contain all of the given values.
criteria.strings.all ("hello", "world")

String Operators

  • =~ Matches a string property which satisfies the given regular expression String.
criteria.aProperty =~ """^(value)|(someting\s+else)"""
  • !~ Matches a string property which does not satisfy the given regular expression String.
criteria.aProperty !~ """\d+"""

Logical Operators

  • ! The unary not operator provides logical negation of an Expression.
!(criteria.aProperty === "value")
  • && Defines logical conjunction (''AND'').
criteria.aProperty === "value" && criteria.another > 0
  • !&& Defines negation of conjunction (''NOR'').
criteria.aProperty === "value" !&& criteria.aProperty @== "other value"
  • || Defines logical disjunction (''OR'').
criteria.aProperty === "value" || criteria.aProperty === "other value"