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Perform aggregation in Foreign Key Column

Default aggregations are not supported in a foreign key column. You can achieve aggregation for the foreign key column by using the custom aggregates. The following example demonstrates the way to achieve aggregation in foreign key column.

In the following example, The Employee Name is a foreign key column and the aggregation for the foreign column was calculated in customAggregateFn.

Source
Preview
index.ts
index.html
import { Grid, ForeignKey, Aggregate, getForeignData, CustomSummaryType, AggregateColumnModel } from '@syncfusion/ej2-grids';
import { data, employeeData } from './datasource.ts';
import { getValue } from '@syncfusion/ej2-base';

Grid.Inject(ForeignKey, Aggregate);

// Custom Aggregate function for foreign column
let customAggregateFn: CustomSummaryType = (data: Object, column: AggregateColumnModel) => {
    return data.result.filter((dObj: Object) => {
        return getValue('FirstName' , getForeignData(grid.getColumnByField(column.columnName), dObj)[0]) === 'Margaret';
    }).length;
};

let grid: Grid = new Grid(
    {
        dataSource: data,
        columns: [
            { field: 'OrderID', headerText: 'Order ID', textAlign: 'Right', width: 100 },
            // Foreign column
            {
                field: 'EmployeeID', headerText: 'Employee Name', width: 150, foreignKeyValue: 'FirstName', dataSource: employeeData,
            },
            { field: 'Freight', headerText: 'Freight', width: 100, textAlign: 'Right'},
            { field: 'ShipName', headerText: 'Ship Name', width: 180 }
        ],
        height: 280,
        aggregates: [
            {
                columns: [
                    {
                        type: 'Custom',
                        customAggregate: customAggregateFn,
                        field: 'EmployeeID',
                        footerTemplate: 'Count of Margaret: ${Custom}'
                    }
                ]
            }
        ]
    });
    grid.appendTo('#Grid');
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