feat: projectionExpression for single table batch get, scan and query

Author: Leandro Díaz Guerra

package-lock.json

@@ -67,6 +67,17 @@ describe('batch get', () => {
       expect(request.params.RequestItems[getTableName(SimpleWithPartitionKeyModel)]).toBeDefined()
       expect(request.params.RequestItems[getTableName(SimpleWithPartitionKeyModel)].ConsistentRead).toBeTruthy()
     })
+
+    it('projection expression', () => {
+      const request = new BatchGetSingleTableRequest<any>(<any>null, SimpleWithPartitionKeyModel, [{ id: 'myId' }])
+      request.projectionExpression('name')
+      expect(request.params.RequestItems).toBeDefined()
+      expect(request.params.RequestItems[getTableName(SimpleWithPartitionKeyModel)]).toBeDefined()
+      expect(request.params.RequestItems[getTableName(SimpleWithPartitionKeyModel)].ProjectionExpression).toBe('#name')
+      expect(request.params.RequestItems[getTableName(SimpleWithPartitionKeyModel)].ExpressionAttributeNames).toEqual({
+        '#name': 'name',
+      })
+    })
   })
 
   describe('should return appropriate value', () => {

src/dynamo/request/batchgetsingletable/batch-get-single-table.request.spec.ts

@@ -11,6 +11,7 @@ import { ModelConstructor } from '../../../model/model-constructor'
 import { batchGetItemsFetchAll } from '../../batchget/batch-get-utils'
 import { BATCH_GET_DEFAULT_TIME_SLOT, BATCH_GET_MAX_REQUEST_ITEM_COUNT } from '../../batchget/batch-get.const'
 import { DynamoDbWrapper } from '../../dynamo-db-wrapper'
+import { resolveAttributeNames } from '../../expression/functions/attribute-names.function'
 import { BaseRequest } from '../base.request'
 import { BatchGetSingleTableResponse } from './batch-get-single-table.response'
 
@@ -39,11 +40,31 @@ export class BatchGetSingleTableRequest<T> extends BaseRequest<
     }
   }
 
+  /**
+   * Determines the read consistency model: If set to true, then the operation uses strongly consistent reads; otherwise, the operation uses eventually consistent reads.
+   */
   consistentRead(value: boolean = true): BatchGetSingleTableRequest<T> {
     this.params.RequestItems[this.tableName].ConsistentRead = value
     return this
   }
 
+  /**
+   * Specifies the list of document attributes to be returned from the table instead of returning the entire document
+   * @param attributesToGet List of document attributes to be returned
+   */
+  projectionExpression(...attributesToGet: string[]): BatchGetSingleTableRequest<T> {
+    // tslint:disable-next-line:no-unnecessary-callback-wrapper
+    const resolved = attributesToGet.map(a => resolveAttributeNames(a))
+    this.params.RequestItems[this.tableName].ProjectionExpression = resolved.map(attr => attr.placeholder).join(', ')
+    Object.values(resolved).forEach(r => {
+      this.params.RequestItems[this.tableName].ExpressionAttributeNames = {
+        ...this.params.RequestItems[this.tableName].ExpressionAttributeNames,
+        ...r.attributeNames,
+      }
+    })
+    return this
+  }
+
   /**
    * fetch all entries and return the raw response (without parsing the attributes to js objects)
    * @param backoffTimer when unprocessed keys are returned the next value of backoffTimer is used to determine how many time slots to wait before doing the next request

src/dynamo/request/batchgetsingletable/batch-get-single-table.request.ts

@@ -8,7 +8,7 @@ import * as DynamoDB from 'aws-sdk/clients/dynamodb'
  */
 export interface BatchGetSingleTableResponse<T> {
   /**
-   * A map of table name to a list of items. Each object in Responses consists of a table name, along with a map of attribute data consisting of the data type and attribute value.
+   * A map of table name to a list of items. Each object in Responses consists of a table name, along with a map of attribute data consisting of the data type and attribute value, as specified by ProjectionExpression.
    */
   Items: T[]
   /**

src/dynamo/request/batchgetsingletable/batch-get-single-table.response.ts

@@ -32,6 +32,10 @@ export class GetRequest<T> extends StandardRequest<T, DynamoDB.GetItemInput, Get
     return this
   }
 
+  /**
+   * Specifies the list of document attributes to be returned from the table instead of returning the entire document
+   * @param attributesToGet List of document attributes to be returned
+   */
   projectionExpression(...attributesToGet: string[]): GetRequest<T> {
     // tslint:disable-next-line:no-unnecessary-callback-wrapper
     const resolved = attributesToGet.map(a => resolveAttributeNames(a))

src/dynamo/request/get/get.request.ts

@@ -9,7 +9,7 @@ import * as DynamoDB from 'aws-sdk/clients/dynamodb'
  */
 export interface QueryResponse<T> {
   /**
-   * An array of item attributes that match the query criteria. Each element in this array consists of an attribute name and the value for that attribute.
+   * An array of item attributes that match the query criteria. Each element in this array consists of an attribute name and the value for that attribute, as specified by ProjectionExpression.
    */
   Items: T[]
   /**

src/dynamo/request/query/query.response.ts

@@ -10,6 +10,7 @@ import { fromDb } from '../../mapper/mapper'
 import { Attributes } from '../../mapper/type/attribute.type'
 import { ModelConstructor } from '../../model/model-constructor'
 import { DynamoDbWrapper } from '../dynamo-db-wrapper'
+import { resolveAttributeNames } from '../expression/functions/attribute-names.function'
 import { and } from '../expression/logical-operator/and.function'
 import { addExpression } from '../expression/param-util'
 import { addCondition } from '../expression/request-expression-builder'
@@ -106,6 +107,20 @@ export abstract class ReadManyRequest<
     return <any>this
   }
 
+  /**
+   * Specifies the list of document attributes to be returned from the table instead of returning the entire document
+   * @param attributesToGet List of document attributes to be returned
+   */
+  projectionExpression(...attributesToGet: string[]): R {
+    // tslint:disable-next-line:no-unnecessary-callback-wrapper
+    const resolved = attributesToGet.map(a => resolveAttributeNames(a))
+    this.params.ProjectionExpression = resolved.map(attr => attr.placeholder).join(', ')
+    Object.values(resolved).forEach(r => {
+      this.params.ExpressionAttributeNames = { ...this.params.ExpressionAttributeNames, ...r.attributeNames }
+    })
+    return <any>this
+  }
+
   /**
    * add a condition for propertyPath
    * @example req.whereAttribute('path.to.prop').eq('value')

src/dynamo/request/read-many.request.ts

@@ -5,7 +5,7 @@ import * as DynamoDB from 'aws-sdk/clients/dynamodb'
 
 export interface ScanResponse<T> {
   /**
-   * An array of item attributes that match the scan criteria. Each element in this array consists of an attribute name and the value for that attribute.
+   * An array of item attributes that match the scan criteria. Each element in this array consists of an attribute name and the value for that attribute, as specified by ProjectionExpression.
    */
   Items: T[]
   /**