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  1. trait Expression {
  2.     def asSQL: (String, Seq[Any])
  3.  
  4.     def %==(other: Expression) = new EqualToExpression(this, other)
  5.     def %!=(other: Expression) = new NotEqualToExpression(this, other)
  6.     def %<(other: Expression) = new SmallerThanExpression(this, other)
  7.     def %>(other: Expression) = new GreaterThanExpression(this, other)
  8.     def %<=(other: Expression) = new SmallerThanOrEqualToExpression(this, other)
  9.     def %>=(other: Expression) = new GreaterThanOrEqualToExpression(this, other)
  10. }
  11.  
  12. class Schema(val name: String)
  13.  
  14. class Relation(val schema: Schema, val name: String)
  15.  
  16. class Attribute(val relation: Relation, val name: String) extends Expression {
  17.     def asSQL =
  18.         (relation.schema.name + "." + relation.name + "." + name, Seq.empty)
  19. }
  20.  
  21. abstract class BinaryExpression(a: Expression, b: Expression, operator: String) extends Expression {
  22.     def asSQL = {
  23.         val (aSQL, bindings1) = a.asSQL
  24.         val (bSQL, bindings2) = b.asSQL
  25.  
  26.         ("(" + aSQL + ") " + operator + " (" + bSQL + ")", bindings1 ++ bindings2)
  27.     }
  28. }
  29.  
  30. class EqualToExpression(a: Expression, b: Expression) extends BinaryExpression(a, b, "=")
  31. class NotEqualToExpression(a: Expression, b: Expression) extends BinaryExpression(a, b, "<>")
  32. class SmallerThanExpression(a: Expression, b: Expression) extends BinaryExpression(a, b, "<")
  33. class GreaterThanExpression(a: Expression, b: Expression) extends BinaryExpression(a, b, ">")
  34. class SmallerThanOrEqualToExpression(a: Expression, b: Expression) extends BinaryExpression(a, b, "<=")
  35. class GreaterThanOrEqualToExpression(a: Expression, b: Expression) extends BinaryExpression(a, b, ">=")
  36.  
  37. class IntExpression(value: Int) extends Expression {
  38.     def asSQL =
  39.         ("?", Array(value))
  40. }
  41.  
  42. class Query(relation: Relation, fields: Seq[Expression], filters: Seq[Expression]) extends Expression {
  43.     def asSQL = {
  44.         val (fieldSQLs, bindings1) = fields.map(_.asSQL).unzip
  45.         val selectStr = "SELECT (" + fieldSQLs.mkString("), (") + ")\n"
  46.  
  47.         val fromStr = s"  FROM ${relation.schema.name}.${relation.name}\n"
  48.  
  49.         val (filterSQLs, bindings2) = filters.map(_.asSQL).unzip
  50.         val whereStr =
  51.             if (filterSQLs.length > 0)
  52.                 " WHERE (" + filterSQLs.mkString(")\n   AND (") + ")\n"
  53.             else
  54.                 ""
  55.  
  56.         (selectStr + fromStr + whereStr, bindings1 ++ bindings2)
  57.     }
  58.  
  59.     def select(newFields: Expression*) =
  60.         new Query(relation, fields ++ newFields, filters)
  61.  
  62.     def where(newFilters: Expression*) =
  63.         new Query(relation, fields, filters ++ newFilters)
  64. }
  65.  
  66. object Query {
  67.     def from(relation: Relation) = new Query(relation, Array[Expression](), Array[Expression]())
  68. }
  69.  
  70. object Main {
  71.     def main(args: Array[String]) {
  72.         val public = new Schema("public")
  73.         val users = new Relation(public, "users")
  74.         val userId = new Attribute(users, "id")
  75.         val userName = new Attribute(users, "name")
  76.         val userEmailAddress = new Attribute(users, "email_address")
  77.         val userAge = new Attribute(users, "age")
  78.  
  79.         val query =
  80.             Query.from(users)
  81.                  .where(userAge %> new IntExpression(20))
  82.                  .select(userId, userName, userEmailAddress)
  83.  
  84.         val (sql, bindings) = query.asSQL
  85.         println(sql)
  86.         bindings.foreach(println(_))
  87.     }
  88. }
  89.  
Success #stdin #stdout 0.39s 382144KB
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SELECT (public.users.id), (public.users.name), (public.users.email_address)
  FROM public.users
 WHERE ((public.users.age) > (?))

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https://ideone.com/8DxMR0
language:
Scala (scala 2.12.8)
created:
12 years ago
visibility:
public

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