Add REMOVE support to the update API

mavericksid · Sep 19, 2016 · 557e2d8 · 557e2d8
1 parent 8b3ca75
commit 557e2d8
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Showing 3 changed files with 30 additions and 7 deletions.
diff --git a/README.md b/README.md
@@ -129,16 +129,16 @@ scala> import com.gu.scanamo.syntax._
 scala> val client = LocalDynamoDB.client()
 scala> import com.amazonaws.services.dynamodbv2.model.ScalarAttributeType._
 scala> val teamTableResult = LocalDynamoDB.createTable(client)("teams")('name -> S)
-scala> case class Team(name: String, goals: Int, scorers: List[String])
+scala> case class Team(name: String, goals: Int, scorers: List[String], mascot: Option[String])
 scala> val teamTable = Table[Team]("teams")
 scala> val operations = for {
-     |   _ <- teamTable.put(Team("Watford", 1, List("Blissett")))
-     |   _ <- teamTable.update('name -> "Watford", set('goals -> 2) and append('scorers -> "Barnes"))
+     |   _ <- teamTable.put(Team("Watford", 1, List("Blissett"), Some("Harry the Hornet")))
+     |   _ <- teamTable.update('name -> "Watford", set('goals -> 2) and append('scorers -> "Barnes") and remove('mascot))
      |   watford <- teamTable.get('name -> "Watford")
      | } yield watford
 
 scala> Scanamo.exec(client)(operations)
-res1: Option[cats.data.Xor[error.DynamoReadError, Team]] = Some(Right(Team(Watford,2,List(Blissett, Barnes))))
+res1: Option[cats.data.Xor[error.DynamoReadError, Team]] = Some(Right(Team(Watford,2,List(Blissett, Barnes),None)))
 ``` 
 
 ### Using Indexes

diff --git a/src/main/scala/com/gu/scanamo/package.scala b/src/main/scala/com/gu/scanamo/package.scala
@@ -59,6 +59,8 @@ package object scanamo {
       AddExpression(fieldValue._1, fieldValue._2)
     def delete[V: DynamoFormat](fieldValue: (Symbol, V)) =
       DeleteExpression(fieldValue._1, fieldValue._2)
+    def remove(field: Symbol) =
+      RemoveExpression(field)
 
     implicit class AndUpdateExpression[X: UpdateExpression](x: X) {
       def and[Y: UpdateExpression](y: Y) = AndUpdate(x, y)

diff --git a/src/main/scala/com/gu/scanamo/update/UpdateExpression.scala b/src/main/scala/com/gu/scanamo/update/UpdateExpression.scala
@@ -14,9 +14,10 @@ import simulacrum.typeclass
 }
 
 sealed trait UpdateType { val op: String }
-final object SET extends UpdateType { override val op = "SET" }
-final object ADD extends UpdateType { override val op = "ADD" }
-final object DELETE extends UpdateType { override val op = "DELETE" }
+case object SET extends UpdateType { override val op = "SET" }
+case object ADD extends UpdateType { override val op = "ADD" }
+case object DELETE extends UpdateType { override val op = "DELETE" }
+case object REMOVE extends UpdateType { override val op = "REMOVE" }
 
 case class SetExpression[V: DynamoFormat](field: Symbol, value: V)
 
@@ -74,6 +75,12 @@ object AddExpression {
     }
 }
 
+/*
+Note the difference between DELETE and REMOVE:
+ - DELETE is used to delete an element from a set
+ - REMOVE is used to remove an attribute from an item
+ */
+
 case class DeleteExpression[V: DynamoFormat](field: Symbol, value: V)
 
 object DeleteExpression {
@@ -88,6 +95,20 @@ object DeleteExpression {
     }
 }
 
+case class RemoveExpression(field: Symbol)
+
+object RemoveExpression {
+  implicit val removeUpdateExpression =
+    new UpdateExpression[RemoveExpression] {
+      override def typeExpressions(t: RemoveExpression): Map[UpdateType, String] =
+        Map(REMOVE -> "#update")
+      override def attributeNames(t: RemoveExpression): Map[String, String] =
+        Map("#update" -> t.field.name)
+      override def attributeValues(t: RemoveExpression): Map[String, AttributeValue] =
+        Map()
+    }
+}
+
 case class AndUpdate[L: UpdateExpression, R: UpdateExpression](l: L, r: R)
 
 object AndUpdate {