Creating Post with Dynamics CRM Web API - odata

Question

A Post entity (https://msdn.microsoft.com/en-us/library/mt607553.aspx) cannot be created using Dynamics CRM 2016 Online Web API.
This payload should create a post on POST /api/data/v8.1/posts
{
"text": "Test Single Post",
"source": 1,
"type": 7
}
(source 1 is an auto post, type 7 is a status post)
But it returns:
{
"error":
{
"code":"",
"message":"An unexpected error occurred.",
"innererror"
{
"message":"An unexpected error occurred..."
}
}
}
Submitting the same payload with only "text" fails too.
Notice that the Post entity does not have single-valued navigation properties (https://msdn.microsoft.com/en-us/library/mt607553.aspx#bkmk_SingleValuedNavigationProperties) that will allow me to set the related entity (contact, account, etc).
For example, Creating a Task entity (https://msdn.microsoft.com/en-us/library/mt607619.aspx) works fine on POST /api/data/v8.1/tasks
{
"subject": "Test Single Task",
"description": "Test One Description of Task",
"regardingobjectid_contact_task#odata.bind": "/contacts(<someguid>)",
"scheduledend": "2016-07-21T12:11:19.4875892Z"
}
It seems to me that Post should expose something like regardingobjectid_contact_post#odata.bind, but it does not.
For context, this is how to create a Post via the SOAP endpoint and the SDK:
var result = Client.getOrganizationService().Create(new Post
{
Text = post.text,
RegardingObjectId = new EntityReference(
entityName,
Guid.Parse(post.regarding_guid)
)
});
Does anyone have a working example of a Post created via the Web API? Is this an omission in the Dynamics CRM Web API?
It doesn't look like this is listed in the limitations: https://msdn.microsoft.com/en-us/library/mt628816.aspx
UPDATE
It appears that the postregarding entity is where the link should be created to contact/account. This can be demonstrated by querying:
/posts?$filter=postregardingid/regardingobjectid_contact/contactid eq <someguid>
However, a "deep insert" like so does not work:
{
"text":"sometext",
"postregardingid":
{
"regardingobjectid_contact#odata.bind":"/contacts(someguid)"
}
}
The response is
Cannot create child entities before parent entity.

Answer 1

Nowhere it's mentioned like Post (activity feed) cannot be created using webapi. In fact it's not listed as crm webapi limitation like you pointed out.
Also on comparison, _regardingobjectid_value lookup property of post is different from activitypointer. Single valued navigation property too.
Out of curiosity, My investigation moved towards the Partner - post_PostRegardings
Only thing making sense - postregarding is strictly internal use. This could be the reason for all such behavior. This is my theory per v8.2 today(Aug 12 2017)
Description: Represents which object an activity feed post is regarding. For internal use only.
Entity Set path:[organization URI]/api/data/v8.2/postregardings
Base Type: crmbaseentity EntityType
Display Name: Post Regarding
Primary Key: postregardingid
Ref: https://msdn.microsoft.com/en-us/library/mt608103.aspx
Update:
Looks like MS recommend the community to use Organization service to create a custom Post record. Web api is still broken. Read more

Answer 2

I was recently struggling with this issue with an Activity table made using powerapps. For those who are interested, here's my post request:
POST: https://<MY_DOMAIN>.crm.dynamics.com/api/data/v9.1/<TABLE_NAME>
{
"regardingobjectid_contact#odata.bind": "/contacts(xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)",
"description": "data for this entity",
"subject": "more data"
}
I didn't do anything different from other peoples' answers. I'll give an update if this problem fails sporadically. But as it is right now, it looks like regardingobjectid may be working in version 9.1

Answer 3

using D365 Api v9.1
POST https://{domain}.crm4.dynamics.com/api/data/v9.1/posts
{
"regardingobjectid_contact#odata.bind":"/contacts(guid)",
"text": "This is a private message post",
"source": 1,
"type": 4
}
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