Update list item multiple lookup value field Microsoft Graph

Question

I am trying to update a multiple lookup value field for a list item.

I tried the following code:

List < QueryOption > options = new List < QueryOption > {
    new QueryOption("$expand", "listitem")
};
//get drive item with list item
var driveItem = graphClient.Sites[IdGestDoc].Drive.Items[itemResult.Id].Request(options).GetAsync().Result;
var fieldValueSet = new FieldValueSet {
    AdditionalData = new Dictionary < string,
    object > {
        {
            "Theme_fonctionnel@odata.type",
            "Collection(Edm.String)"
        }, {
            "Theme_fonctionnel", ThemeFonctionnel.ToArray()
        } //ThemeFonctionnel is a List<string> => lookupid
    }
};
await graphClient.Sites[IdGestDoc].Lists["Documents"].Items[driveItem.ListItem.Id].Fields.Request().UpdateAsync(fieldValueSet);

But this code don't work and I don't find what I am missing. Any help will be appreciated !

Answer 1

To set a Lookup field, you need to set the property by passing in the property name and the addition 'LookupId':

        string propertyName = "Theme_fonctionnel";

        var fieldValueSet = new FieldValueSet();

        var propertyValuesArray = options.ToArray();

        var attributes = new Dictionary<string, object>();

        //first, we need to specify the input data type
        string oDataTypeInfoPropertyName = propertyName + "LookupId@odata.type";
        string oDataDataType = "Collection(Edm.String)";
        attributes.Add(oDataTypeInfoPropertyName, oDataDataType);

        //next, we need to pass the values as an array
        string newPropertyName = propertyName + "LookupId";
        attributes.Add(newPropertyName, propertyValuesArray);

        fieldValueSet.AdditionalData = attributes;