Angular 4 - apply if else condition for formModel angular

i have a check box

<cm-checkbox [(ngMode)]="form.true" id="1" name="form1">
</cm-checkbox>

for all the rows in a table.

main check box -

<cm-checkbox [(ngMode)]="form.true" id="1" name="form2">
</cm-checkbox>

by default the check boxes are selected as value is true. I can select with inputs property like true, false, default true, required, value - all boolean types. and output property as checkboxchange type eventemitter. but im not getting how proceed further for the requirement.

i am looking for one main checkbox on the top so that if i select that all rows checkboxes should be selected. And If i deselect the main checkbox then all should be deselected. But i can select rows checkboxes individually as well. any idea.