CODEWITHSUNDEEP
c#mongodb
raresm
raresm

Reputation: 423

Do not insert field if null or empty

I have a C# class with some fields and some of them are null. Those that are null I do not want to be inserted into db with null value. I do not want them inserted into db at all. How do I achieve that?

class User
{
    public string FirstName;
    public string LastName;
    public string MidName;
}

Not every user has a MidName, but Mongo inserts into db with null value on MidName field.

Upvotes: 14

Views: 16630

Answers (3)

Tallons
Tallons

Reputation: 71

The best solution I could come up with to prevent the insertion of Null & Empty values was by creating a custom Attribute that inherits the IBsonMemberMapAttribute interface and uses the BsonMemberMap.SetShouldSerializeMethod() method. Both come from the MongoDB.Bson.Serialization namespace which comes from the MongoDb.Driver Nuget Package.

Step 1: Create the Custom Attribute

// BsonIgnoreIfNullOrEmptyAttribute.cs
using MongoDB.Bson.Serialization;
using System.Collections;

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
public class BsonIgnoreIfNullOrEmptyAttribute : Attribute, IBsonMemberMapAttribute
{

  public void Apply(BsonMemberMap memberMap)
  {
     _ = memberMap.SetShouldSerializeMethod(classObj =>
     {
        string propertyName = memberMap.MemberName;
        var propertyValue = classObj?.GetType().GetProperty(propertyName).GetValue(classObj);

        return propertyValue switch
        {
            null => false,
            string value when string.IsNullOrEmpty(value) => false,
            ICollection collection when collection.Count == 0 => false,
            _ => true
        };
     });
  }

}

Explanation: Inside the Apply() method, I used memberMap.MemberName which gives you the propertyName of the property that has the [BsonIgnoreIfNullOrEmpty] Attribute and then I used reflections to get the value of that property when it is read by the MongoDB's IBsonSerializer (which is determined by the BsonClassMap). Next, I created a switch expression that will validate the value of the property and check if the value is null or empty for string and ICollection types. Note: Returning false inside the SetShouldSerializeMethod() method means that it will NOT serialize the property.

Step 2: Use the Custom Attribute on the desired properties.

It will behave similarly to the other [BsonIgnore...] Attributes

// User.cs
using MongoDB.Bson.Serialization.Attributes;

public class User
{
    [BsonIgnoreIfDefault]
    public Guid Id { get; set; }
    [BsonIgnoreIfNullOrEmpty]
    public string FirstName { get; set; }
    [BsonIgnoreIfNullOrEmpty]
    public string LastName { get; set; }
    [BsonIgnoreIfNullOrEmpty]
    public string MiddleName { get; set; }
    [BsonIgnoreIfDefault]
    public int Age { get; set; }
    [BsonIgnoreIfDefault]
    public DateTime BirthDate { get; set; }
    [BsonIgnoreIfNull]
    public Department Department  { get; set; }
    [BsonIgnoreIfNullOrEmpty]
    public List<Guid> FriendIds { get; set; }
}

Upvotes: 0

CodeCaster
CodeCaster

Reputation: 151586

Using the aptly named [BsonIgnoreIfNull] attribute:

class User
{
    public string FirstName;
    public string LastName;
    [BsonIgnoreIfNull]
    public string MidName;
}

Upvotes: 24

Tony
Tony

Reputation: 17637

Ensure you are registering the new convention pack early enough. If any classes have already been mapped before you register the new convention pack they won't be updated.

Here's my test code:

public class C
{
    public int Id { get; set; }
    public string S { get; set; }
}

public static class Program
{
    public static void Main(string[] args)
    {
        ConventionRegistry.Register(
            "Ignore null values",
            new ConventionPack
            {
                new IgnoreIfNullConvention(true)
            },
            t => true);

        var client = new MongoClient("mongodb://localhost");
        var server = client.GetServer();
        var database = server.GetDatabase("test");
        var collection = database.GetCollection<C>("test");

        collection.Drop();
        collection.Insert(new C { Id = 1, S = null });

        Console.WriteLine("Press Enter to continue.");
        Console.ReadLine();
    }
}

The following document was inserted into the database:

db.test.find()

{ "_id" : 1 }

Source: https://groups.google.com/forum/#!topic/mongodb-user/7-NFXBNeEXs

Upvotes: 12

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