SOLR Spell checker not working well with multiple words

Question

I'm using Solr 7.2.1, I'm trying to implement the 'Did you mean' feature, I've configured the spell check handler and it's working well, the issue is when trying with multiple words, if only one word was spelled correctly, no results are returned. For example if I write 'drive caq', it returns me empty results, if I write 'caq' as a single word, it returns me the correctly spelled word which is 'car'. I want it t return me correctly spelled collations as 'drive car'

Solr Configurations:

<searchComponent name="spellcheck" class="solr.SpellCheckComponent">
    <str name="queryAnalyzerFieldType">text_general</str>
    <lst name="spellchecker">
      <str name="name">default</str>
      <str name="field">title</str>
      <str name="classname">solr.DirectSolrSpellChecker</str>
      <str name="distanceMeasure">internal</str>
      <float name="accuracy">0.5</float>
      <int name="maxEdits">2</int>
      <int name="minPrefix">1</int>
      <int name="maxInspections">5</int>
      <int name="minQueryLength">3</int>
      <float name="maxQueryFrequency">0.5</float>
    </lst>
  </searchComponent>

<requestHandler name="/spell" class="solr.SearchHandler" startup="lazy">
    <lst name="defaults">
      <str name="spellcheck.dictionary">default</str>
      <str name="spellcheck">on</str>
      <str name="df">title</str>
      <str name="spellcheck.extendedResults">true</str>
      <str name="spellcheck.count">10</str>
      <str name="spellcheck.alternativeTermCount">5</str>
      <str name="spellcheck.maxResultsForSuggest">5</str>
      <str name="spellcheck.collate">true</str>
      <str name="spellcheck.collateExtendedResults">true</str>
      <str name="spellcheck.maxCollationTries">10</str>
      <str name="spellcheck.maxCollations">5</str>
      <str name="spellcheck.build">true</str> 
    </lst>
    <arr name="last-components">
      <str>spellcheck</str>
    </arr>
  </requestHandler>

the code for using the spell check component:

  using (IProviderSearchContext ctx = ContentSearchManager.GetIndex("sitecore_sxa_master_index").CreateSearchContext())
                {
                    var results = ctx.GetSpellCheck(new SolrQuery(Term), new SpellCheckHandlerQueryOptions()
                    {
                        SpellCheck = new SpellCheckingParameters()
                        {
                            Count = 10,
                            Build = true,
                            Collate = true
                        }
                    });
                }

Answer 1

Replace

<str name="classname">solr.DirectSolrSpellChecker</str>

with

<str name="classname">solr.WordBreakSolrSpellChecker</str>

in <searchComponent name="spellcheck"> node of solrconfig.xml

rebuild dictionary and request spell checking like:

var results = ctx.GetSpellCheck(new SolrQuery(Term), new SpellCheckHandlerQueryOptions()
{
    SpellCheck = new SpellCheckingParameters()
    {
        Count = 10,
        Build = true,
        Collate = true
    }
});

if (results != null && results.SpellChecking != null && results.SpellChecking.Count > 0)
{
    var words = terms.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
    if (words.Length < 2)
    {
        return results.SpellChecking.SelectMany(x => x.Suggestions);
    }

    var correct = "";
    foreach (var w in words)
    {
        var suggest = results.SpellChecking.FirstOrDefault(x => x.Query.Equals(w));
        if (suggest != null && suggest.Suggestions.Any())
        {
            correct += suggest.Suggestions.First() + " ";
        }
        else
        {
            correct += w + " ";
        }
    }
    return new List<string> { correct.Trim() };
}
return new List<string>();

Update

As you mentioned in comments, /spell?q=title:term works only if term is one word. It is not so. When you spell checking by multiple words you can catch error undefined field _text_ because it is default configuration of <initParams path="/spell>. Just relpace initparams for spellchecking in solrconfig.xml with:

  <initParams path="/spell">
    <lst name="defaults">
      <str name="df">title</str>
    </lst>
  </initParams>

Your query to Solr will look similar to

/spell?q=:word1 word2 word3&start=0&rows=5&fl=title&fq=_indexname:(your_index_name)&spellcheck=true&spellcheck.count=5

and it should works fine (it works for me).

I also noticed that your use field name title without any postfix, it is ok if it is your custom configuration. If not, your should use it with postfix like title_t (the same name as you see in solr) in all definitions in solrconfig.xml.