Use compareWith function from Angular Material mat-select component with linked firebase value

Question

I'm trying to edit some member's firebase data with a mat-select component composed of different types.

I'm not sure with my structure of nodes but I did this :

member:
    member1:
        name: 
        types:
            typekey1 : Title1
            typekey3 : Title3
            ...

types:
    typekey1:
        key: typekey1
        title: Title1
    typekey2:
        key: typekey2
        title: Title2
    typekey3:
        key: typekey3
        title: Title3   
    ...                 

So I can't make the following function

compareFn(t1: Type, t2: Type): boolean { 
return t1 && t2 ? t1.key === t2.key : t1 === t2;
}

to work with the template

<mat-form-field>
<mat-select [compareWith]="compareFn" [(ngModel)]="member.types" multiple>
<mat-option 
    *ngFor="let type of types | async" 
    [value]="type">
    {{type.title}}
</mat-option>

I can't seem to find the way to connect the two kind of type in the compareFn function and have selected the option when the component is launched

Answer 1

For an object of the following structure:

listOfObjs = [{ name: 'john', id: '1'}, { name: 'jimmy', id: '2'},...]

Define markup like this:

<mat-form-field>
  <mat-select
    [compareWith]="compareObjects"
    [(ngModel)]="obj">
       <mat-option  *ngFor="let obj of listOfObjs" [value]="obj">
          {{ obj.name }}
       </mat-option>
    </mat-select>
</mat-form-field>

And define comparison function like this:

compareObjects(o1: any, o2: any) {
  if(o1.name == o2.name && o1.id == o2.id )
  return true;
  else return false
}

Answer 2

Here is the example:

<mat-select [compareWith]="compareFn" [(ngModel)]="defaultItem">
    <mat-option *ngFor="let country of countries" [value]="item">
        {{country.name}}
    </mat-option>
</mat-select>

compareFn(c1: Country, c2: Country): boolean {
    return c1 && c2 ? c1.id === c2.id : c1 === c2;
}

Ref: I have answered here, https://stackoverflow.com/a/63539749/10373693