ElasticSearch NEST: Bulk-indexing operation does not make use of specified document IDs

Elastic Stack Elasticsearch
2

The "Id" on an ExpandoObject is not a property of the type, but a key in the underlying IDictionary<string,object> that ExpandoObject is backed by.

You can see this by reflecting over the properties of ExpandoObject with

dynamic expandoObject = JsonConvert.DeserializeObject<ExpandoObject>(@"{
		""IndexId"": ""dummyindex"",
		""Id"": ""0c2d48bd-6842-4f15-b7f2-57fa259b0642"",
		""UserId"": ""dummy_user_1"",
		""Country"": ""dummy_stan""
	}
");

Type t = expandoObject.GetType();
PropertyInfo[] properties = t.GetProperties(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
foreach (PropertyInfo property in properties)
{
	Console.WriteLine(property.ToString());
}

which prints

System.Dynamic.ExpandoClass Class
System.Collections.Generic.ICollection`1[System.String] System.Collections.Generic.IDictionary<System.String,System.Object>.Keys
System.Collections.Generic.ICollection`1[System.Object] System.Collections.Generic.IDictionary<System.String,System.Object>.Values
System.Object System.Collections.Generic.IDictionary<System.String,System.Object>.Item [System.String]
Int32 System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<System.String,System.Object>>.Count
Boolean System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<System.String,System.Object>>.IsReadOnly

To solve your issue, you can specify the Id for each document however by passing the second delegate argument to .IndexMany()

dynamic expandoObject = JsonConvert.DeserializeObject<ExpandoObject>(@"{
		""IndexId"": ""dummyindex"",
		""Id"": ""0c2d48bd-6842-4f15-b7f2-57fa259b0642"",
		""UserId"": ""dummy_user_1"",
		""Country"": ""dummy_stan""
	}
");

var bulkResponse = client.Bulk(bu => bu
    .IndexMany(new[] { expandoObject }, (b, d) => b.Id((Id)d.Id))
);

The cast of d.Id to Id (or could have been string as that is the actual type, but casting to Id will use the implicit conversion from string to Id) is required because d is a dynamic type and the runtime is unable to dispatch without it.