NEST aggs collection is read only - elasticsearch

Question

I'm using the NEST client with the following syntax:
_server.Search<Document>(s => s.Index(_config.SearchIndex)
.Query(q => q.MatchAll(p => p)).Aggregations(
a => a
.Terms("type", st => st
.Field(p => p.Type)
)));
However I keep getting the following exception
A first chance exception of type 'System.NotSupportedException' occurred in mscorlib.dll
Additional information: Collection is read-only.
It only seems to occur when I'm using aggregations, the field of Type has the following mapping:
[Keyword(Name = "Type")]
public string Type { get; set; }

Answer 1

I would double check the versions of NEST and Elasticsearch.Net that you are using. I just tried the following example with Elasticsearch 5.1.2 and NEST 5.0.1 and don't see the issue
void Main()
{
var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var defaultIndex = "default-index";
var connectionSettings = new ConnectionSettings(pool)
.DefaultIndex(defaultIndex);
var client = new ElasticClient(connectionSettings);
if (client.IndexExists(defaultIndex).Exists)
client.DeleteIndex(defaultIndex);
client.CreateIndex(defaultIndex, c => c
.Mappings(m => m
.Map<Document>(mm => mm.AutoMap())
)
);
var documents = Enumerable.Range(1, 100).Select(i =>
new Document
{
Type = $"Type {i % 5}"
}
);
client.IndexMany(documents);
client.Refresh(defaultIndex);
var searchResponse = client.Search<Document>(s => s
.Index(defaultIndex)
.Query(q => q.MatchAll(p => p))
.Aggregations(a => a
.Terms("type", st => st
.Field(p => p.Type)
)
)
);
foreach (var bucket in searchResponse.Aggs.Terms("type").Buckets)
Console.WriteLine($"key: {bucket.Key}, count {bucket.DocCount}");
}
public class Document
{
[Keyword(Name = "Type")]
public string Type { get; set; }
}
this outputs
key: Type 0, count 20
key: Type 1, count 20
key: Type 2, count 20
key: Type 3, count 20
key: Type 4, count 20