ERROR Solr Error : [undefined field content_type] - upgarding from Sitecore 8.2 to 10.1 and from Lucene to Solr

Question

I'm working on a Sitecore upgrade from 8.2 to 10.1, which includes replacing Lucene with Solr. I have a content listing page that allows filtering by content type as well as many other fields - these are OOTB Sitecore fields, not computed. I have this SearchResultItem defined:

public class ContentTypeSearchResultItem : Sitecore.ContentSearch.SearchTypes.SearchResultItem
{
    [Sitecore.ContentSearch.IndexField("region_sm")]
    [TypeConverter(typeof(IndexFieldEnumerableConverter))]
    public Guid Region { get; set; }

    [Sitecore.ContentSearch.IndexField("content_type_sm")]
    [TypeConverter(typeof(IndexFieldEnumerableConverter))]
    public IEnumerable<Guid> ContentType { get; set; }

 
}

One thing I changed initially was that the names had no suffixes, so I changed "content_type" to "content_type_sm" (this was after I got the Undefined error the first time)

My fields exist in Solr:

and in fact in another place in the site where I pull all items with a particular template ID, when I inspect the items while debugging, I can drill into the fields and see that they have the "content_type_sm" field and it is properly populated.

But on the listing page, my query which uses this code:

var contentTypePredicate = PredicateBuilder.True<ContentTypeSearchResultItem>();
foreach (var taxonomy in taxonomies)
{
     contentTypePredicate = contentTypePredicate.Or(x => x.ContentType.Contains(taxonomy));
}
predicate = predicate.And(contentTypePredicate);

...returns no results and I see the error in my logs, ERROR Solr Error : [undefined field content_type]

EDIT:

Manually updating the fieldMap fixed the issue:

<field fieldName="content_type" returnType="stringCollection"></field>

Answer 1

As discussed in the comments, there is no need to add the "_sm" in ContentTypeSearchResultItem.

In your latest update, it looks like you are trying to map a stringcollection to an IEnumerable < Guid >

Please can you try changing index config to:

<field fieldName="content_type" returnType="guidCollection"></field>

And then update your SearchResult to:

[Sitecore.ContentSearch.IndexField("content_type")]
[TypeConverter(typeof(IndexFieldEnumerableConverter))]
public IEnumerable<Guid> ContentType { get; set; }

You will need to repopulate and rebuild the index.