Angularfire2可观察的concat无法正常工作

Question

This is what my data looks like:

{
  "Category" : {
    "-KVuXp30tdhR1CqmCb_X" : {
      "name" : "Category1",
      "parentCategoryId" : ""
  },
    "-KVuY0CjGePvUo2qVcGb" : {
      "name" : "Category2",
      "parentCategoryId" : ""
  },
    "-KW9U76wJg-4hgnMUvu2" : {
      "name" : "Category1sub1",
      "parentCategoryId" : "-KVuXp30tdhR1CqmCb_X"
  },
    "-KYODOJXjqnRMkVSsIFs" : {
      "name" : "Category2Sub1",
      "parentCategoryId" : "-KVuY0CjGePvUo2qVcGb"
  },
    "-KYOKdbX22UCeU2EZcYQ" : {
      "name" : "Category1Sub3",
      "parentCategoryId" : "-KVuXp30tdhR1CqmCb_X"
  },
    "-KYOM3dV9pX0Isx-7V5C" : {
      "name" : "Category2Sub2",
      "parentCategoryId" : "-KVuY0CjGePvUo2qVcGb"
  }
 }
}

I want to list under main categories and sub categories.

• Category1
• Category2
• Category1 >> Category1sub1
• Category2 >> Category2Sub1
• Category1 >> Category1Sub3
• Category2 >> Category2Sub2

The sample code here (plunker) .

What am I doing wrong. How do i do it.

Thanks.

Answer 1

AngularFire 's list method returns Observabel that never ends so there is no point in using it in concat . If you want to get only first value you should use take .

There is no db property on your service, hence

this.db.object

will throw an error (you didn't see an error because that code hadn't been executed).

Look at this plunker and ask if something is not clear.