Create index with completion suggest using Nest elasticsearch

Question

I am using elasticsearc 2.3.3 and Nest 2.3.2, I need to create index. Need to map the properties with attributes added in the class file.

public class IndexDocument
{
    [Number(Store = true)]
    public long Id { get; set; }
    [String(Store = true, Index = FieldIndexOption.Analyzed, TermVector = TermVectorOption.WithPositionsOffsets)]
    public string Title { get; set; }
    public Attachment File { get; set; }
    [String(Store = true, Index = FieldIndexOption.Analyzed)]
    public string DocumentType { get; set; }
    [String(Store = true, Index = FieldIndexOption.NotAnalyzed)]
    public string DocLocation { get; set; }
    [String(Store = true, Index = FieldIndexOption.Analyzed)]
    public DateTime LastModifiedDate { get; set; }

}

public class Attachment
{
    public Attachment()
    {

    }
    [String(Name = "_content_length", Store = true, Index = FieldIndexOption.Analyzed)]
    public long ContentLength { get; set; }
    [String(Store = true, Index = FieldIndexOption.Analyzed, TermVector = TermVectorOption.WithPositionsOffsets, Name = "_content")]
    public string Content { get; set; }

}

Also I would like to add a completion suggest to the File field. I am new in this elastic search. Can anyone please help?

I have created my attachment index as below. How to append completion suggest and stemmer code with this?

this.client.CreateIndex("mydocs", c => c.Mappings(mp => mp.Map<IndexDocument>
                (m => m.Properties(ps => ps.Attachment
                        (a => a.Name(o => o.File)
                               .TitleField(t => t.Name(x => x.Title).TermVector(TermVectorOption.WithPositionsOffsets))
                               )))));