How do you get the objects that don't have a certain field in them?

Question

function setup() {
 myRequest = indexedDB.deleteDatabase('myDatabase')
 myRequest.onsuccess = function() {
  var myRequest
  
  myRequest = indexedDB.open('myDatabase')
  myRequest.onupgradeneeded = function(response) {
   var myDatabase
    ,myObjectStore
   
   myDatabase = response.target.result
   myObjectStore = myDatabase.createObjectStore('myData',{autoIncrement:true})
   myObjectStore.createIndex('myIndex', 'field2') 
  }
  myRequest.onerror = function(response) {
   debugger
  }
  myRequest.onsuccess = function(response) {
   var myTransaction
    ,myObjectStore
    ,myRequest
    ,obj = {}
   window.myDatabase = response.target.result
   myTransaction = myDatabase.transaction(['myData'],'readwrite')
   myObjectStore = myTransaction.objectStore('myData')
   obj.field1 = 'a'
   obj.field2 = 'b'
   myObjectStore.add(obj)
   obj = {}
   obj.field1 = 'c'
   myObjectStore.add(obj)
  }
 }
}
setup()

function myFunction() {
 var myTransaction = myDatabase.transaction(['myData'])
 var myObjectStore = myTransaction.objectStore('myData')
 var myIndex = myObjectStore.index('myIndex')
 // The following line is where I need help:
 var myRange = IDBKeyRange.only(null)
 // I'm trying to get the objects where field2 doesn't exist.
 var myRequest = myIndex.openCursor(myRange)
 myRequest.onsuccess = function(response) {
  result = response.target.result
  if (result) {
   console.log(result)
   result.continue()
  }
 }
 
}
</script>

<a href="javaScript:myFunction();">click here</a>

Answer 1

You cannot do this in a straightforward way. There is no way to query for missing/empty fields.

However, you can be clever and work around this.

1. Before storing an object in an object store, check if the object's property is empty (null/undefined/empty string/etc). If the field is missing, set a separate field like 'otherPropertyIsMissing' to a value. I suggest using an empty string ('') or 0. If the property is not missing, delete the 'otherPropertyIsMissing' property.
2. Add an index to the object store in the onupgradeneeded method on the 'otherPropertyIsMissing' property. For example, name it 'indexOnOtherPropertyIsMissing'.
3. Query against the index 'indexOnOtherPropertyIsMissing' for all objects. This query will only return objects where the 'indexOnOtherPropertyIsMissing' property is not missing. This set of objects is all objects where the other property is missing.