Criteria4s

Criteria4s is a simple domain-specific language (DSL) to define criteria and predicate expressions for any data stores by using Scala type class mechanisms in a type-safe way. It pretends to be agnostic to any data store, and it is extensible to support any kind of data stores.

Formal Definition of the Expressions

The formal definition of the Criteria4s' type-classes (expressions) is as follows:

Criteria    :=  Conjuction Criteria Criteria | Predicate | Value<Boolean>
Predicate   :=  UnaryPred Ref | BinaryPred Ref Ref
Ref         :=  Value<T> | Col
Conjuction  :=  AND | OR
UnaryPred   :=  IS_NULL | IS_NOT_NULL ...
BinaryPred  :=  EQ | NEQ | GT | LT | GEQ | LEQ | IN | LIKE ...

Where:

• Criteria is the main expression of the DSL
• Conjuction is the conjunction operator expression
• UnaryPredOp is the unary predicate operator expression
• BinaryPredOp is the binary predicate operator expression
• Ref is a reference to a value or a column
• Value<T> is a value expression of a certain type T
• Col is a column expression

Getting Started

To use dsl of Criteria4s, you need to add the following dependency to your project:

SonaType Repository

• Core library: criteria4s-core
• SQL implementation: criteria4s-sql
• MongoDB dialect implementation: criteria4s-mongodb

SBT

libraryDependencies += "io.github.rafafrdz" %% "criteria4s-core" % "<version>" // Core library
libraryDependencies += "io.github.rafafrdz" %% "criteria4s-sql" % "<version>" // SQL implementation
libraryDependencies += "io.github.rafafrdz" %% "criteria4s-mongodb" % "<version>" // MongoDB implementation

Maven

<!-- Core library -->
<dependencies>
    <dependency>
        <groupId>io.github.rafafrdz</groupId>
        <artifactId>criteria4s-core_2.13</artifactId>
        <version>0.8.2</version>
    </dependency>

    <!-- SQL implementation -->
    <dependency>
        <groupId>io.github.rafafrdz</groupId>
        <artifactId>criteria4s-core_2.13</artifactId>
        <version>0.8.2</version>
    </dependency>

    <!-- MongoDB implementation -->
    <dependency>
        <groupId>io.github.rafafrdz</groupId>
        <artifactId>criteria4s-mongodb_2.13</artifactId>
        <version>0.8.2</version>
    </dependency>
</dependencies>

Important

Criteria4s is a work in progress and it is not ready for production use. Also, it is just available for Scala 2.13.

Dialects

Criteria4s is extensible to support any kind of data stores. Currently, it supports the following dialects:

Dialect	Package
SQL	sql
MongoDB	mongodb
PostgresSQL	postgresql

Examples

Here, we will show some examples of how to use the Criteria DSL. You can find more examples in the criteria4s-examples module.

Imports

First, we need to import the Criteria4s DSL and the SQL dialect:

import io.github.rafafrdz.criteria4s.core._
import io.github.rafafrdz.criteria4s.examples.datastores._
import io.github.rafafrdz.criteria4s.extensions._
import io.github.rafafrdz.criteria4s.functions._

Defining Criteria Expressions

We can define criteria expressions in a polymorphic way by using the Criteria DSL. You can find more definitions examples in the Defining Criteria Expressions document.

def expr[T <: CriteriaTag : LEQ : EQ : AND : OR : Show[Column, *]]: Criteria[T] =
  (col[T]("field1") leq lit(3)) and (col[T]("field2") leq lit(4)) or (col[T]("field3") === lit("c"))

Case of use

def ageCriteria[T <: CriteriaTag : GT : LT : AND : Show[Column, *]]: Criteria[T] =
  (col[T]("age") gt lit(18)) and (col[T]("age") lt lit(65))

def refCriteria[T <: CriteriaTag : EQ : Show[Column, *]](fieldName: String, id: UUID): Criteria[T] =
  col[T](fieldName) === lit(id.toString)

Evaluating Criteria Expressions

And then we can use those expressions defined belows in order to generate criteria expressions for different datastores by importing the corresponding dialects. You can find evaluation examples for some different dialects in the following documents:

• PostgreSQL Dialect
• MongoDB Dialect
• MySQL Dialect
• Custom Dialect

Inline Criteria DSL

Or maybe we can use the Criteria DSL inline:

(col[PostgreSQL]("field1") leq lit(3)) and (col[PostgreSQL]("field2") leq lit(4)) or (col[PostgreSQL]("field3") === lit("c"))
// res: (('field1' <= 3) AND ('field2' <= 4)) OR ('field3' = c)

(col[MongoDB]("field1") leq lit(3)) and (col[MongoDB]("field2") leq lit(4)) or (col[MongoDB]("field3") === lit("c"))
// res: {$or: [{$and: [{"field1": {$lte: 3}}, {"field2": {$lte: 4}}]}, {"field3": {$eq: c}}]}

(col[WeirdDatastore]("field1") leq lit(3)) and (col[WeirdDatastore]("field2") leq lit(4)) or (col[WeirdDatastore]("field3") === lit("c"))
// res: {left: {left: {left: field1, opt: <=, right: 3 }, opt: AND, right: {left: field2, opt: <=, right: 4 } }, opt: OR, right: {left: field3, opt: =, right: c } }