How to get user from User field LookupId - api

Question

I have a list in sharepoint online.
And in this list, i have a person field.
When i call the API endpoint to get all the items in the list, i get an LookupId value for the person field.
I tried to get the user by using the value of the lookupid, but it don't work because the id is not recognized.
The lookupid is a int (eg: 21) instead of a guid.
Is there something missing in the configuration of the person field or in my calls to Microsoft Graph API ?

Answer 1

When a user signs into a SharePoint site collection for the first time, a ListItem is created in a hidden User Information List. The LookupId in a PersonOrGroup field refers to the ListItem in this list. The URL for the User Information List for SharePoint Online should be:
https://{yourTenant}.sharepoint.com/{yourSiteCollection}/_catalogs/users/detail.aspx
Since the User Information List is a generic SharePoint list, you can query the list via Graph. First, get the list id for the User Information List. An easy way to get the list id is to view the source for the User Information Site via Chrome and search for 'listId'. You should find a result like this:
"listId":"{yourListIdIsHere}"
Copy the id. By using the copied id, the id of your root site and the LookupId, you can get the ListItem in the User Information List:
https://graph.microsoft.com/v1.0/sites/{siteId}/lists/{pasteCopiedListId}/items/{lookUpId}?$expand=Fields
The ListItem contains information about the user, such as the email, which can be used to identify the Azure user:
https://graph.microsoft.com/v1.0/users/{eMail}
Question: How could i get the hidden User Information List from Microsoft Graph?
If you do not want to use the 'trick' with Google Chrome to get the id, there is another way to get the site. Typically, if you want to get the id for any site, you would call:
https://graph.microsoft.com/v1.0/sites/{siteId}/lists
However, you will not find the id of the User Information List, even if you include hidden sites. I do not know why. An additional problem seems to be, that you cannot filter lists by their name:
https://graph.microsoft.com/v1.0/sites/{siteId}/lists?$filter=name eq 'users'
The query returns an error, that the provided filter statement is not supported. The only way to get the list without knowing the id seems to by using the property displayName of the list. However, the displayName is based on your localization. So, since I am from Germany, I can get the site by using the query:
https://graph.microsoft.com/v1.0/sites/{siteId}/lists?$filter=displayName eq 'Benutzerinformationsliste'
You will need to replace Benutzerinformationsliste with your localized name. For EN replace it with 'User Information List'.
This returns the expected result:
{
"#odata.context": "https://graph.microsoft.com/v1.0/$metadata#sites('xxx')/lists(id,name,displayName)",
"value": [
{
"#odata.etag": "\"xxx\"",
"id": "xxx",
"name": "users",
"displayName": "Benutzerinformationsliste"
}
]
}
As you can see, the name of the list is 'users', so why the first filter statement does not work is a little mystery to me. Maybe someone here knows and can help out.

Answer 2

Some of the queries above don't work at the moment.
What I finally found as a good solution - after trying many many queries - is that you can do this by following the few steps below:
1- Get the GUID of the user information list.
Using the title of the list "User Information List" or the name "users" in the parameter "$filter" does not work.
Don't forget 'system' among the properties you select if you want to retrieve the hidden system-lists.
GET https://graph.microsoft.com/v1.0/sites('{site_id}')/lists?select=id,name,system
2- Filter the previous result in order to pick up the ID of the targeted list named 'users'.
By the way, applying this restriction "$filter=name eq 'users'" does not work.
You will get an exception. So you must do the filtering part by writing a few lines of code.
3- Once you've got the list identifier, then select all the items you want. And voilà! The word 'Fields' must be in pascal case (uppercase the first letter ).
GET https://graph.microsoft.com/v1.0/sites('{site_id}')/lists('users_list_id')/items?$select=Fields&$expand=Fields

Answer 3

As #QuestionsPS1991 mentioned, the people field in fact refers to the hidden user list. With the lookupid, we can get the user via below methods:
Get user by id
Get user property by expanding lookup field
//////////// updated
By default, MS Graph does not return this user list. You may hard code the list id or follow ##QuestionsPS1991 suggestion. Below is my test: