How to base an inner NgFor on the outter NgFor in Angular

Question

I'm trying to display a list of conversations in my Angular app, & then display the messages contained within those various conversations underneath each Conversation Title .

Here is my latest code -

HTML:

<div
   class="card"
   style="width: 18rem;"
   *ngFor="let conversation of myConversations"
>
<div class="card-body">
    <h5 class="card-title">{{ conversation.conversationTitle }}</h5>
    <h6 class="card-subtitle mb-2 text-muted">
       Conversation ID: {{ conversation.conversationId }}
    </h6>
    <p *ngFor="let message of myConversationMessages" class="card-text">
       {{ message.messageText }}
    </p>
</div>

TS:

myConversations: IConversation[] = [];
myConversationMessage: IConversationMessages = {
conversationId: 0,
messageId: 0,
messageText: ''
}; 
myConversationMessages: IConversationMessages[] = [];
constructor(private conversationService: ConversationService) {}

ngOnInit() {
this.conversationService.getConversations().subscribe(conversations => {
  this.myConversations = conversations;
  this.displayMessages();
});
}

displayMessages() {
for (let i of this.myConversations) {
  for (let j of i.messages) {
    this.myConversationMessages.push({
        conversationId: i.conversationId,
        messageId: j.messageId,
        messageText: j.messageText
    });
  }
}
console.log(this.myConversationMessages);
}

This is what I'm currently able to display at the moment:

Each conversation has it's own card, but the messages are being repeated for all conversations, regardless of which conversation they're connected to.

I think I need to make some change to the inner ngFor , but I'm not exactly sure which change to make. Any ideas on what changes are required? Thanks!

Also, here is the associated JSON:

[
  {
    "conversationId": 1,
    "conversationTitle": "My first convo",
    "messages": [
      {
        "messageId": 1,
        "messageText": "Hi"
      },
      {
        "messageId": 2,
        "messageText": "Hello"
      }
    ]
  },
  {
    "conversationId": 2,
    "conversationTitle": "My second convo",
    "messages": [
      {
        "messageId": 1,
        "messageText": "test"
      },
      {
        "messageId": 2,
        "messageText": "testing"
      }
    ]
  }
]

Answer 1

Based of the JSON you have provided you should be able to use an *ngfor , inside the *ngfor to read the messages. I have stripped away some of the elements but the following should give you the result you need. Based of the JSON in the question.

Solution

<div class="card" style="width: 18rem;" *ngFor="let conversation of myConversations">
    <div class="card-body">
        <h5 class="card-title">
            {{ conversation.conversationTitle }}
        </h5>

        <h6 class="card-subtitle mb-2 text-muted"> Conversation ID:
            {{ conversation.conversationId }}
        </h6>

        <div *ngFor="let message of conversation.messages" class="card-text">
            <span>
                {{ message.messageText }}
            </span>
        </div>
    </div>
</div>

If the JSON is the initial myConversations then you will not need to do anything more with that data as it is already enough to work with.