Hello Reader

I  have a Custom object  (called API_Order__c) which has  lookup  field to Account
My plan is  to insert  MULTIPLE  records  in 1  REST API call and I am trying to build  the good JSON
I am not able to do this. I tried  the stanbdard REST  and I tried  to  use the COmposite/tree  REST

Seee below what I havew tried:

TEST 1

I want to  create  1 record  using REST command AND I want to reference the Account with External ID.
I use the below  REST
Method: POST
URL: /services/data/v39.0/sobjects/API_Order__c/

{
  "SourceFile__c" : "DE_1A_MSV3",
  "Order_Date__c" : "2017-07-07",
  "Account__r" : 
         {
         "External_ID_vod__c":"WDEF01663170"
         },
  "Account_Name__c" : "Adler-Apotheke",
  "NumberOfExpectedItemLines__c" : "2", 
  "External_Id__c" : "API_O_1003"
}

this is WORKING

​TEST 2
BUT  if I want to insert  MULTIPLE  records  I do not  know  what is  the right syntax


[
{
  "SourceFile__c" : "Value 1",
  "Order_Date__c" : "2017-07-07",
  "Account__r" : 
         {
         "External_ID_vod__c":"XXXX"
         },
  "External_Id__c" : "API_O_1003"
},
{
  "SourceFile__c" : "Value 2",
  "Order_Date__c" : "2017-07-08",
  "Account__r" : 
         {
         "External_ID_vod__c":"YYYY"
         },
  "External_Id__c" : "API_O_1003"
}
]

I god  JSON parsng ERROR

TEST 3

I tried to use  the COMPOSITE  REST  call  to insert Multiple records and if I am passing the Salesforce ID  of  the  Account lookup is OK 

POST
/services/data/v39.0/composite/tree/API_Order__c

{
"records" :[
  {
  "attributes" : {"type" : "API_Order__c", "referenceId" : "ref1"},
  "SourceFile__c" : "DE_1A_MSV3",
  "Order_Date__c" : "2017-07-07",
  "Account__c" : "0015E000004jH2I"
  }, 
  {
  "attributes" : {"type" : "API_Order__c", "referenceId" : "ref2"},
  "SourceFile__c" : "Val2",
  "Order_Date__c" : "2017-07-07",
  "Account__c" : "0015E000004jH2I"
   }]
}

TEST 4
BUT IF  I TRY  TO REFERENC ETHE ACCOUNT WITH EXTER NAL ID  I FAIL

POST
/services/data/v39.0/composite/tree/API_Order__c

{
"records" :[
  {
  "attributes" : {"type" : "API_Order__c", "referenceId" : "ref1"},
  "SourceFile__c" : "DE_1A_MSV3",
  "Order_Date__c" : "2017-07-07",
  "Account__r" : 
         {
         "External_ID_vod__c":"WDEF01663170"
         },
  "Account_Name__c" : "Adler-Apotheke",
  "NumberOfExpectedItemLines__c" : "2", 
  "External_Id__c" : "API_O_1001"
  },
  {
  "attributes" : {"type" : "API_Order__c", "referenceId" : "ref2"},
  "SourceFile__c" : "DE_1A_MSV3",
  "Order_Date__c" : "2017-07-07",
  "Account__r" : 
         {
         "External_ID_vod__c":"WDEF01663170"
         },
  "Account_Name__c" : "Adler-Apotheke",
  "NumberOfExpectedItemLines__c" : "2",
  "External_Id__c" : "API_O_1002"
   }]
}

I have the ERROR  message: Cannot reference a foreign key field Account__r.


Any help?  

Thanks in advance Csaba