How to Set Up MongoDB Class Maps for C# for Optimal Query Performance and Storage Size

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public class BlogPost
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{
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  // ...
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  [BsonElement("title")]
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  public string Title { get; set; } = string.Empty;
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  // ...
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}

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{
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  // ...
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  "title": "Blog post title",
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  // ...
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}

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BsonClassMap.RegisterClassMap<BlogPost>(cm =>
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{
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  cm.AutoMap();
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  cm.MapMember(x => x.Title).SetElementName("title");
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});

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var pack = new ConventionPack();
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pack.Add(new CamelCaseElementNameConvention());
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ConventionRegistry.Register(
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  "Camel Case Convention",
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  pack, 
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  t => true);

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public class BlogPost
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{
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  [BsonRepresentation(BsonType.ObjectId)]
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  public string Id { get; set; } = ObjectId.GenerateNewId().ToString();
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  // ...
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  [BsonRepresentation(BsonType.ObjectId)]
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  public ICollection<string> TopComments { get; set; } = new List<string>();
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}

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{ 
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  "_id" : ObjectId("6569b12c6240d94108a10d20"), 
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  // ...
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  "TopComments" : [
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    ObjectId("6569b12c6240d94108a10d21"), 
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    ObjectId("6569b12c6240d94108a10d22")
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  ] 
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}

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BsonDefaults.GuidRepresentationMode 
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= GuidRepresentationMode.V3;

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[BsonGuidRepresentation(GuidRepresentation.Standard)]
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public Guid MyGuid { get; set; } = Guid.NewGuid();

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[BsonIgnoreExtraElements]
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public class BlogPost 
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{
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  // ...
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}

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var pack = new ConventionPack();
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pack.Add(new IgnoreExtraElementsConvention(true));
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ConventionRegistry.Register(
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  "Ignore Extra Elements Convention",
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  pack, 
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  t => true);

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public class BlogPost
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{
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  // ...
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  [BsonExtraElements()]
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  public IDictionary<string, object> ExtraElements { get; set; } = new Dictionary<string, object>();
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}

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public class BlogPost
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{
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  // ...
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  public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
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  public DateTime? UpdatedAt { get; set; }
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  public DateTime LastChangeAt => UpdatedAt ?? CreatedAt;
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}

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public class BlogPost
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{
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  // ...
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  public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
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  public DateTime? UpdatedAt { get; set; }
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  [BsonElement()]
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  public DateTime LastChangeAt => UpdatedAt ?? CreatedAt;
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}

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{ 
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  // ...
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  "CreatedAt" : ISODate("2023-12-01T12:16:34.441Z"), 
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  "UpdatedAt" : null, 
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  "LastChangeAt" : ISODate("2023-12-01T12:16:34.441Z") 
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}

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BsonClassMap.RegisterClassMap<BlogPost>(cm =>
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{
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  // Perform auto-mapping to include properties 
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  // without specific mappings
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  cm.AutoMap();
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  // Serialize string as ObjectId
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  cm.MapIdMember(x => x.Id)
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    .SetSerializer(new StringSerializer(BsonType.ObjectId));
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  // Serialize ICollection<string> as array of ObjectIds
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  cm.MapMember(x => x.TopComments)
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    .SetSerializer(
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       new IEnumerableDeserializingAsCollectionSerializer<ICollection<string>, string, List<string>>(
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         new StringSerializer(BsonType.ObjectId)));
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  // Change member name
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  cm.MapMember(x => x.Title).SetElementName("title");
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  // Serialize Guid as binary subtype 4
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  cm.MapMember(x => x.MyGuid).SetSerializer(new GuidSerializer(GuidRepresentation.Standard));
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  // Store extra members in dictionary
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  cm.MapExtraElementsMember(x => x.ExtraElements);
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  // Include read-only property
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  cm.MapMember(x => x.LastChangeAt);
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});