Unable to update single or multiple lookup values with rest api

Question

I have a list name "Parts", This list has a lookupfield called Parts and it look into the Parts list.

Aka 1 part can contain other parts. Hope you get the Idea

When I'm trying to update the LookUpField with either a single value or multiple values, I get an error.

An unexpected 'PrimitiveValue' node was found when reading from the JSON reader. A 'StartObject' node was expected.

I have tried the following:

 var customerData = { 
    __metadata: { 'type': 'SP.Data.'+Type+'ListItem' }, 
    Title: Title, 
    Image: {Description:'',Url: Image},
    Parts: 7
}; 

---

var customerData = { 
    __metadata: { 'type': 'SP.Data.'+Type+'ListItem' }, 
    Title: Title, 
    Image: {Description:'',Url: Image},
    PartsId: 7
}; 

---

var customerData = { 
    __metadata: { 'type': 'SP.Data.'+Type+'ListItem' }, 
    Title: Title, 
    Image: {Description:'',Url: Image},
    PartsId: {'results': 7}
}; 

---

var customerData = { 
    __metadata: { 'type': 'SP.Data.'+Type+'ListItem' }, 
    Title: Title, 
    Image: {Description:'',Url: Image},
    PartsId: {'results': [7] }
}; 

I keep getting the same Error no matter what I try. I've made sure that i have an item with id 7;

Here is the complete code:

var requestUri = _spPageContextInfo.webAbsoluteUrl + '/_api/Web/Lists/getByTitle(\''+Type+'\')/items('+id+')';
var requestHeaders = { 
    'Accept': 'application/json;odata=verbose', 
    'X-RequestDigest': $('#__REQUESTDIGEST').val(), 
    'X-HTTP-Method': 'MERGE',
    'If-Match': '*'
}; 
var customerData = { 
    __metadata: { 'type': 'SP.Data.'+Type+'ListItem' }, 
    Title: Title, 
    Image: {Description:'',Url: Image},
    PartsId: 7
}; 
requestBody = JSON.stringify(customerData); 
$.ajax({ url: requestUri, type: 'POST', 
    contentType: 'application/json;odata=verbose', headers: requestHeaders, 
    data: JSON.stringify(customerData)
,
success: function (response)
{ 

    $(".check").attr("class", "check check-complete success");
    $(".fill").attr("class", "fill fill-complete success");
    $(".path").attr("class", "path path-complete");

    setTimeout(
        function() 
        {
            closeDialog();
        }, 2000);
}, 
error: function(error)
{ 
    console.log(error)
} 
});

If i only use Title and Image then it works just fine.

Answer 1

Hello try with following,

var customerData = { 
"__metadata": { "type": 'SP.Data.'+Type+'ListItem' }, 
"Title": "Abc",     
"PartsId": {"results": [7] }
};