Merge pull request #123 from shiftcode/#16-updateExpression-ifnotexists

feat(update): ifNotExists option for update.set

Author: michaelwittwer

src/dynamo/expression/prepare-and-add-update-expressions.function.spec.ts

@@ -53,6 +53,19 @@ describe('PrepareExpressions function', () => {
         })
       })
 
+      it('set (ifNotExists)', () => {
+        const now = new Date()
+
+        prepareAndAddUpdateExpressions(metadata, params, [update<UpdateModel>('lastUpdated').set(now, true)])
+        expect(params.UpdateExpression).toBe('SET #lastUpdated = if_not_exists(#lastUpdated, :lastUpdated)')
+        expect(params.ExpressionAttributeNames).toEqual({ '#lastUpdated': 'lastUpdated' })
+        expect(params.ExpressionAttributeValues).toEqual({
+          ':lastUpdated': {
+            S: now.toISOString(),
+          },
+        })
+      })
+
       it('set (nested map)', () => {
         prepareAndAddUpdateExpressions(metadata, params, [update('info.details').set('the new detail')])
         expect(params.UpdateExpression).toBe('SET #info.#details = :info__details')

src/dynamo/expression/type/update-expression-definition-chain.ts

@@ -16,7 +16,7 @@ export interface UpdateExpressionDefinitionChainTyped<T, K extends keyof T> {
    * - persons.age
    * - places[0].address.street
    */
-  set: (value: T[K]) => UpdateExpressionDefinitionFunction
+  set: (value: T[K], ifNotExists?: boolean) => UpdateExpressionDefinitionFunction
 
   /**
    * appends one or more values to the start or end of a list, value must be of type L(ist)
@@ -78,7 +78,7 @@ export interface UpdateExpressionDefinitionChain {
    * - persons.age
    * - places[0].address.street
    */
-  set: (value: any) => UpdateExpressionDefinitionFunction
+  set: (value: any, ifNotExists?: boolean) => UpdateExpressionDefinitionFunction
 
   /**
    * appends one or more values to the start or end of a list, value must be of type L(ist)

src/dynamo/expression/update-expression-builder.ts

@@ -84,7 +84,12 @@ function buildDefaultExpression(
       statement = `${namePlaceholder} = ${namePlaceholder} - ${valuePlaceholder}`
       break
     case 'set':
-      statement = `${namePlaceholder} = ${valuePlaceholder}`
+      const ifNotExists = values.length > 1 && !!values[values.length - 1] || false
+      if (ifNotExists) {
+        statement = `${namePlaceholder} = if_not_exists(${namePlaceholder}, ${valuePlaceholder})`
+      } else {
+        statement = `${namePlaceholder} = ${valuePlaceholder}`
+      }
       break
     case 'appendToList':
       const position = values.length > 1 ? values[values.length - 1] || 'END' : 'END'