When server operations are enabled information from the DataSource is sent from the client to the server about current page, grouping, sorting and etc expressions. In order to modify the request parameters in suitable format for your server you can use the transport.parameterMap.
The format which DataSource requires the grouped items to be in is similar to the following:
//name of the field on which data is grouped
// value of the current group
items: [item1, item2, item3]
// there are multiple nested groups and items collection contains groups instead of the actual items
In case your server returns data in a different format, schema object's group function can be use to transform the data. Please refer to the schema.groups
Indeed it expects the total amount of items to be returned as number. as well Since there is serverPaging enabled only items for the current pages will be returned, but it does need information about the number of all records.
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