Question

我在MongoDB中有一个较长的二进制Blob（实际上是一个存储的PNG，带有微型图像）。我需要一个过滤器，该过滤器将返回所有带有非空blob的子弹。

我尝试过这样的事情：

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);

但是这将返回空集。如果将Filter更改为Filter.Empty，我将收到收藏中的所有子弹。

集合定义如下：

[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;
}

Answer 1

空byte数组将以"content_mini" : BinData(0,"")的形式存储在MongoDB中，因此您可以简单地使用$ne在Mongo shell中构建查询

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

要使用C＃构建该查询，您需要Builders泛型和Ne方法。要过滤掉所有空数组和null值，可以使用以下代码：

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();

您不应使用Filter.Empty，因为它实际上代表了空查询，就像Mongo Shell中的db.col.find({})

MongoDB筛选器，以检查二进制字段是否为空

1 个答案: