DynamoDB Query

Overview

The DynamoDB Query Snap retrieves data from DynamoDB by executing a DynamoDB Query via the REST API.

It processes Snap properties and formats the HTTP request entity body according to the syntax defined in the AWS DynamoDB Query API Reference. It can be used to retrieve data from DynamoDB table as well as Global Secondary Index or Local Secondary Index.



Supported Accounts

Prerequisites

None.

Snap views

Type Description Examples of upstream and downstream Snaps
Input

This Snap has at most one document input view.

If the upstream Snap is connected, this Snap executes once per each input document and produces the query results as a stream of documents to the output view. Each input document is used to evaluate expression properties in the Snap.
Output

This Snap has exactly one document output view and produces a stream of documents, one for each item matching the query criteria.
Learn more about Error handling.

Snap settings

Note: Learn about the common controls in the Snap settings dialog.
Field/Field set Description

Label

String 		Required.Specify a unique name for the Snap. Modify this to be more appropriate, especially if there are more than one of the same Snap in the pipeline.

Default value: DynamoDB Query

Table name

String/Expression/ Suggestion 		Required. The name of the DynamoDB table. Table names can be suggested if the expression property is disabled. The input document schema and pipeline parameters can be suggested when the expression property is enabled.

Default value: None

Example: EmployeeEvents, $TableName, _TableName

Secondary index name

String/Expression/ Suggestion 		The name of Global Secondary Index or Local Secondary Index if used in the query. Amazon DynamoDB provides fast access to items in a table by specifying primary key values. However, many applications might benefit from having one or more secondary (or alternate) keys available, to allow efficient access to data with attributes other than the primary key. For more information, see Improving Data Access with Secondary Indexes.

Default value: None

Example: EffectiveDate-index, $secondary_index, _secondary_index

Projection expression

String/Expression 		A string that identifies one or more attributes to retrieve from the table. The attributes in the expression must be separated by commas. If no attribute names are specified, then all attributes will be returned. If any of the requested attributes are not found, they will not appear in the result.

Default value: None

Example: EffectiveDate, EmpID, EventID, #name, or $attributes, or _attributes

Key condition expression

String/Expression 		The condition that specifies the key value(s) for items to be retrieved by the Query action. The condition must perform an equality test on a single partition key value. The condition can also perform one of several comparison tests on a single sort key value. Query can use KeyConditionExpression to retrieve one item with a given partition key value and sort key value, or several items that have the same partition key value but different sort key values. Refer to the KeyConditionExpression section in the AWS DynamoDB Query API Reference for more details.

Default value: None

Example: EffectiveDate = :val1

Filter expression

String/Expression

A string that contains conditions that DynamoDB applies after the Query operation, but before the data is returned to the Snap. Items that do not satisfy the filter expression criteria are not returned. A filter expression does not allow key attributes. You cannot define a filter expression based on a partition key or a sort key.

Note: A filter expression is applied after the items have already been read; the process of filtering does not consume any additional read capacity units. For more information, see the Filter Expression for Query section in Working with Queries.

Default value: None

Example: #v >= :num

Expression attribute values

Specify the placeholders for the Expression Attribute Names and/or Expression Attribute Values.

Example: If your table contains a column named UUID (a reserved word) and you want to read a value from the UUID column, then you must assign a placeholder for the column name because you cannot use a reserved word directly in your expression. You can define the Attribute #u, leave the Type blank, and enter the value as UUID. In the Snap Filter expression condition, enter Set #u=:val1. :val1 is the placeholder for the value in the table which is defined as Attribute :val1 of Type B with ValuedGhpcyB0ZXh0I.

Note: DynamoDB reserves certain words and they are called reserved words. You must not use reserved words as attribute names in expressions. If you must write an expression that contains a word that conflicts with a DynamoDB reserved word, then you can define an expression attribute name to use in the place of the reserved word. For more information, see Expression Attribute Names. Similarly, you cannot use certain values as attribute values in expressions and instead must define an expression attribute name. For more information, see Expression Attribute Values.
Attribute

String/Expression		 The expression attribute name. Begins with a # for names and : for values.

Default value: None

Example: :val1, #U
Type

String/Expression		 The attribute type. Blank for Expression Attribute Names. S for string, N for number, and so on, for Values.

Default value: None

Example: B
Value

String/Expression		 The actual literal to be used in the query condition.

Default value: None

Example: 13, UUID

Action

Dropdown list 		Enter COUNT to get only the number of items after query execution or DESCRIBE TABLE to get the table metadata at the output view, or QUERY for normal query operations.

Default value: QUERY

Example: QUERY, COUNT, DESCRIBE TABLE

Consistent read

Checkbox 		Determines the read consistency model. If set to true, then the operation uses strongly consistent reads. Otherwise, the operation uses eventually consistent reads. Strongly consistent reads are not supported on global secondary indexes. If you query a global secondary index with Consistent read set to true, you will receive an Exception.

Default value: Not selected

Pass through

Checkbox 		If true, the input document is passed through to the output view under the 'original' key.

Default value: Not selected

Snap execution

Dropdown list
Choose one of the three modes in which the Snap executes. Available options are:
  • Validate & Execute: Performs limited execution of the Snap and generates a data preview during pipeline validation. Subsequently, performs full execution of the Snap (unlimited records) during pipeline runtime.
  • Execute only: Performs full execution of the Snap during pipeline execution without generating preview data.
  • Disabled: Disables the Snap and all Snaps that are downstream from it.

Default value: Execute only

Troubleshooting

The Snap produces an error document if DynamoDB fails to execute the submitted query. The request_entity field in the error document contains the HTTP entity body of the submitted query and may be useful when troubleshooting the pipeline. The Snap processes the Snap properties and prepares the HTTP entity body for the query. The error_entity field in the error document is the error message from the DynamoDB server describing which part of the query has caused the error.