CODEWITHSUNDEEP
c#databasemongodb
PiotrK
PiotrK

Reputation: 4453

MongoDB Filter to check if binary field is not empty

I have long binary blob (a stored PNG actually with miniature) in MongoDB. I need a filter that will return all slugs with non-empty blob.

I tried something like this:

var f = Builders<Common.Json.Database.Picture>.Filter.Where(pic => pic.ContentMini.Length > 0 && pic.ContentFull.Length > 0);
var p = Builders<Common.Json.Database.Picture>.Projection.Include(x => x.Slug);
var s = Builders<Common.Json.Database.Picture>.Sort.Ascending(x => x.Slug);

return Collections.Pictures.Find(f)
                            .Project<Common.Json.Database.Picture>(p)
                            .Sort(s)
                            .ToList()
                            .Select(x => x.Slug);

But this returns empty set. If I change Filter to Filter.Empty I am recieving all slugs in my collection.

The collection definition is below:

[System.Serializable]
public class Picture
{
    [BsonId]
    [JsonIgnore]
    [NonSerialized]
    public ObjectId InternalId;

    [BsonElement("slug")]
    [JsonProperty("slug")]
    public string Slug;

    [BsonElement("author")]
    [JsonProperty("author")]
    public Common.Author Author;

    [BsonElement("owner")]
    [BsonRepresentation(BsonType.String)]
    [JsonProperty("owner")]
    public Guid OwningUserOrGroup;

    [BsonElement("keywords")]
    [JsonProperty("keywords")]
    public List<string> Keywords = new List<string>();

    [BsonElement("last_updated")]
    [JsonProperty("last_updated")]
    public DateTime LastUpdated;

    [BsonElement("is_approved")]
    [JsonProperty("is_approved")]
    public bool IsApproved;

    [BsonElement("is_obsolete")]
    [JsonProperty("is_obsolete")]
    public bool IsObsolete;

    [BsonElement("content_mini")]
    [BsonRepresentation(BsonType.Binary)]
    [JsonIgnore]
    public byte[] ContentMini;

    [BsonElement("content_full")]
    [BsonRepresentation(BsonType.Binary)]
    [JsonIgnore]
    public byte[] ContentFull;
}

Upvotes: 1

Views: 1546

Answers (1)

mickl
mickl

Reputation: 49975

Empty byte array gets stored in MongoDB as "content_mini" : BinData(0,"") so you can simply use $ne to build your query in Mongo shell

db.pictures.find( {"content_mini": { $ne: new BinData(0,"") } } )

To build that query in C# you need Builders generic type and Ne method. To filter out all empty arrays and null values you can use below code:

var filter = Builders<Picture>.Filter.Ne(f => f.ContentMini, new byte[] { });
var filter2 = Builders<Picture>.Filter.Ne(f => f.ContentMini, null);
var result = Col.Find(filter & filter2).ToList();

You shouldn't use Filter.Empty because it actaully represents empty query, just like db.col.find({}) in Mongo shell

Upvotes: 2

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