Adding blog post item category with REST API Sharepoint 2013

Question

I want to insert a billet item list with related category ID in REST API Sharepoint.

I proceeded as follows:

POST /_api/lists/getbytitle('Billets')/items

{
    "__metadata": { "type": "SP.Data.BilletsListItem" },
    "Title": "Mise à jour",
    "PublishedDate": "2016-05-06T10:52:00Z",
    "Body": "test",
    "PostCategory": 2
    }
}

Error:

{
  "error": {
    "code": "-1, Microsoft.SharePoint.Client.InvalidClientQueryException",
    "message": {
      "lang": "fr-FR",
      "value": "Un nœud 'PrimitiveValue' avec une valeur non-Null a été trouvé lors de la tentative de lecture de la valeur d'une propriété de navigation ; pourtant, un nœud 'StartArray', un nœud 'StartObject' ou un nœud 'PrimitiveValue' avec une valeur Null était attendu."
    }
  }
}

Without PostCategory parameter in the JSON the item is added successfully but without category.

Here the description of PostCategory field :

    "__metadata": {
      "id": "/_api/Web/Lists(guid'd67d1f54-aab5-460d-905d-a904553975e6')/Fields(guid'38bea83b-350a-1a6e-f34a-93a6af31338b')",
      "uri": "/_api/Web/Lists(guid'd67d1f54-aab5-460d-905d-a904553975e6')/Fields(guid'38bea83b-350a-1a6e-f34a-93a6af31338b')",
      "type": "SP.FieldLookup"
    },
    "CanBeDeleted": false,
    "DefaultValue": null,
    "Description": "",
    "Direction": "none",
    "EnforceUniqueValues": false,
    "EntityPropertyName": "PostCategory",
    "Filterable": true,
    "FromBaseType": false,
    "Group": "Colonnes personnalisées",
    "Hidden": false,
    "Id": "38bea83b-350a-1a6e-f34a-93a6af31338b",
    "Indexed": false,
    "InternalName": "PostCategory",
    "JSLink": "clienttemplates.js",
    "ReadOnlyField": false,
    "Required": false,
    "SchemaXml": "<Field Name=\"PostCategory\" Type=\"LookupMulti\" DisplayName=\"Catégorie\" List=\"{81E335A6-8361-4883-A835-C5E1C6B0E67B}\" Mult=\"TRUE\" ShowField=\"Title\" ID=\"{38bea83b-350a-1a6e-f34a-93a6af31338b}\" Sortable=\"FALSE\" Sealed=\"TRUE\" SourceID=\"http://schemas.microsoft.com/sharepoint/v3\" StaticName=\"PostCategory\" ColName=\"int2\" RowOrdinal=\"0\" />",
    "Scope": "/Lists/Billets",
    "Sealed": true,
    "Sortable": false,
    "StaticName": "PostCategory",
    "Title": "Catégorie",
    "FieldTypeKind": 7,
    "TypeAsString": "LookupMulti",
    "TypeDisplayName": "Recherche",
    "TypeShortDescription": "Recherche (informations déjà sur ce site)",
    "ValidationFormula": null,
    "ValidationMessage": null,
    "AllowMultipleValues": true,
    "IsRelationship": true,
    "LookupField": "Title",
    "LookupList": "{81E335A6-8361-4883-A835-C5E1C6B0E67B}",
    "LookupWebId": "74bab6ac-e483-456b-9a8a-7c7fb279c4b7",
    "PrimaryFieldId": null,
    "RelationshipDeleteBehavior": 0
  }

How can I add category Id in my post JSON request ?

Answer 1

I have found! Here solve my problem :

POST /_api/lists/getbytitle('Billets')/items

{
    "__metadata": { "type": "SP.Data.BilletsListItem" },
    "Title": "Mise à jour",
    "PublishedDate": "2016-05-06T10:52:00Z",
    "Body": "test",
    "PostCategoryId": {"results": [2]}
}