Type system (request mapping) - Amazon AppSync
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Type system (request mapping)

When using the Amazon AppSync DynamoDB resolver to call your DynamoDB tables, Amazon AppSync needs to know the type of each value to use in that call. This is because DynamoDB supports more type primitives than GraphQL or JSON (such as sets and binary data). Amazon AppSync needs some hints when translating between GraphQL and DynamoDB, otherwise it would have to make some assumptions on how data is structured in your table.

For more information about DynamoDB data types, see the DynamoDB Data type descriptors and Data types documentation.

A DynamoDB value is represented by a JSON object containing a single key-value pair. The key specifies the DynamoDB type, and the value specifies the value itself. In the following example, the key S denotes that the value is a string, and the value identifier is the string value itself.

{ "S" : "identifier" }

Note that the JSON object cannot have more than one key-value pair. If more than one key-value pair is specified, the request mapping document isn’t parsed.

A DynamoDB value is used anywhere in a request mapping document where you need to specify a value. Some places where you need to do this include: key and attributeValue sections, and the expressionValues section of expression sections. In the following example, the DynamoDB String value identifier is being assigned to the id field in a key section (perhaps in a GetItem request mapping document).

"key" : {
   "id" : { "S" : "identifier" }
}

Supported Types

Amazon AppSync supports the following DynamoDB scalar, document, and set types:

String type S

A single string value. A DynamoDB String value is denoted by:

{ "S" : "some string" }

An example usage is:

"key" : {
   "id" : { "S" : "some string" }
}
String set type SS

A set of string values. A DynamoDB String Set value is denoted by:

{ "SS" : [ "first value", "second value", ... ] }

An example usage is:

"attributeValues" : {
   "phoneNumbers" : { "SS" : [ "+1 555 123 4567", "+1 555 234 5678" ] }
}
Number type N

A single numeric value. A DynamoDB Number value is denoted by:

{ "N" : 1234 }

An example usage is:

"expressionValues" : {
   ":expectedVersion" : { "N" : 1 }
}
Number set type NS

A set of number values. A DynamoDB Number Set value is denoted by:

{ "NS" : [ 1, 2.3, 4 ... ] }

An example usage is:

"attributeValues" : {
   "sensorReadings" : { "NS" : [ 67.8, 12.2, 70 ] }
}
Binary type B

A binary value. A DynamoDB Binary value is denoted by:

{ "B" : "SGVsbG8sIFdvcmxkIQo=" }

Note that the value is actually a string, where the string is the base64-encoded representation of the binary data. Amazon AppSync decodes this string back into its binary value before sending it to DynamoDB. Amazon AppSync uses the base64 decoding scheme as defined by RFC 2045: any character that isn’t in the base64 alphabet is ignored.

An example usage is:

"attributeValues" : {
   "binaryMessage" : { "B" : "SGVsbG8sIFdvcmxkIQo=" }
}
Binary set type BS

A set of binary values. A DynamoDB Binary Set value is denoted by:

{ "BS" : [ "SGVsbG8sIFdvcmxkIQo=", "SG93IGFyZSB5b3U/Cg==" ... ] }

Note that the value is actually a string, where the string is the base64-encoded representation of the binary data. Amazon AppSync decodes this string back into its binary value before sending it to DynamoDB. Amazon AppSync uses the base64 decoding scheme as defined by RFC 2045: any character that is not in the base64 alphabet is ignored.

An example usage is:

"attributeValues" : {
   "binaryMessages" : { "BS" : [ "SGVsbG8sIFdvcmxkIQo=", "SG93IGFyZSB5b3U/Cg==" ] }
}
Boolean type BOOL

A Boolean value. A DynamoDB Boolean value is denoted by:

{ "BOOL" : true }

Note that only true and false are valid values.

An example usage is:

"attributeValues" : {
   "orderComplete" : { "BOOL" : false }
}
List type L

A list of any other supported DynamoDB value. A DynamoDB List value is denoted by:

{ "L" : [ ... ] }

Note that the value is a compound value, where the list can contain zero or more of any supported DynamoDB value (including other lists). The list can also contain a mix of different types.

An example usage is:

{ "L" : [
      { "S"  : "A string value" },
      { "N"  : 1 },
      { "SS" : [ "Another string value", "Even more string values!" ] }
   ]
}
Map type M

Representing an unordered collection of key-value pairs of other supported DynamoDB values. A DynamoDB Map value is denoted by:

{ "M" : { ... } }

Note that a map can contain zero or more key-value pairs. The key must be a string, and the value can be any supported DynamoDB value (including other maps). The map can also contain a mix of different types.

An example usage is:

{ "M" : {
      "someString" : { "S"  : "A string value" },
      "someNumber" : { "N"  : 1 },
      "stringSet"  : { "SS" : [ "Another string value", "Even more string values!" ] }
   }
}
Null type NULL

A null value. A DynamoDB Null value is denoted by:

{ "NULL" : null }

An example usage is:

"attributeValues" : {
   "phoneNumbers" : { "NULL" : null }
}

For more information about each type, see the DynamoDB documentation .