Force.com Apex Code Developer's Guide
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Aggregation for Lightning Connect Custom Adapters
If you receive a COUNT() query, the selected
column has the value QueryAggregation.COUNT in its
aggregation property. The selected column is
provided in the columnsSelected property on the
tableSelection for the DataSource.QueryContext.
The following example illustrates how to apply the value of the aggregation property to handle COUNT() queries.
1// Handle COUNT() queries
2if (context.tableSelection.columnsSelected.size() == 1 &&
3 context.tableSelection.columnsSelected.get(0).aggregation ==
4 QueryAggregation.COUNT) {
5 List<Map<String, Object>> countResponse = new List<Map<String, Object>>();
6 Map<String, Object> countRow = new Map<String, Object>();
7 countRow.put(context.tableSelection.columnsSelected.get(0).columnName,
8 response.size());
9 countResponse.add(countRow);
10 return countResponse;
11}An aggregate query can still have filters, so your query method can be implemented like the following example to support basic aggregation queries, with or without filters.
1override global DataSource.TableResult query(DataSource.QueryContext context) {
2 List<Map<String,Object>> rows = retrieveData(context);
3 List<Map<String,Object>> response = postFilterRecords(
4 context.tableSelection.filter, rows);
5 if (context.tableSelection.columnsSelected.size() == 1 &&
6 context.tableSelection.columnsSelected.get(0).aggregation ==
7 DataSource.QueryAggregation.COUNT) {
8 List<Map<String, Object>> countResponse = new List<Map<String,
9 Object>>();
10 Map<String, Object> countRow = new Map<String, Object>();
11 countRow.put(context.tableSelection.columnsSelected.get(0).columnName,
12 response.size());
13 countResponse.add(countRow);
14 return DataSource.TableResult.get(context, countResponse);
15 }
16 return DataSource.TableResult.get(context, response);
17}