Canvas Reserved Keywords and Predefined Objects

Following are the list of keywords and predefined objects that can be provided by you in the Request JSON Configuration field.

S.No	Canvas Keyword	Alias Name to be provided by the User	Description
1	`$sort.field`	sortField	Used to identify the field chosen for sorting.
2	`$sort.datatype`	sortDatatype	Used to identify the data type of the field chosen for sorting.
3	`$sort.direction`	sortDirection	Used to identify the sorting direction (ascending or descending) of the field.
4	`$page.end`	pageEnd	Used to indicate the index end.
5	`$page.size`	pageSize	Used to indicate the number of records to be fetched from the starting index.
6	`$page.start`	pageStart	Used to indicate the starting index of the records fetched.
7	`$context.accessToken`	accessToken	This is a predefined object containing the value of the access token for the service. This is useful in JSON configuration if we want to pass the value of token in a particular field.
8	`$context.apiKey`	apiKey	This is a predefined object containing the value of the API key for the service. This is useful in JSON configuration if we want to pass the value of token in a particular field.
9	`$filter.value1`	filterValue1	The field value searched by the user.
10	`$filter.value2`	filterValue2	The second field value searched by the user (in case of a range of values).
11	`$filter.fieldName`	filterFieldName	The column ID of the field which must be filtered.
12	`$filter.Operator`	filterOperator	The search condition used to filter the field data (for example, =, >, <, and so on).
13	`$filter.datatype`	filterDatatype	The data type of the field value (string, date, int, and so on).
14	`$filter`	filter	It is a predefined object which contains the array of runtime filters specified by the user.
15	`$extraParams`	extraParams	It is a predefined object which contains the array of extra parameters obtained as a request.
16	`$request`	request	It is a predefined object which contains the request parameters.
17	`$user`	user	It is a predefined object which contains the user number, ID, and GCIF.
18	`$session`	session	It is a predefined object which contains the session attributes.
19	`$userPref`	userPref	It is a predefined object which contains the user preferences.
20	`$context`	context	Master object consisting of all the predefined objects such as $request, $user, $filter.Operator, currentUserNo, currentGCIF, and so on.
21	`$response`	response	It's a predefined object which contains the parameters available in the response to the request to fetch data for view.
22	$form	form	This is a predefined object that contains the form data submitted by the end user.

Keywords used for Canvas internal purpose are as follows:

S.No	Canvas Keyword	Description
1	inheritModel	Used to combine logical JSON blocks.
2	ignoreKey	Used to indicate that a particular field (key) must be ignored in the combined JSON.
3	mergeKey	Used to indicate that a particular field (key) must be added in the combined JSON.
4	function	The function specified in the metadata has the logic to tweak the JSON. For example, we will have to iterate through the filter array and prepare the JSON objects before adding the objects to the JSON payload. This logic is provided as a sample implementation in Canvas as 'andFilter' method in the DefaultRestServiceInstruction.java class.