Question

我正在dotnetcore 2.1中使用MongoDB.Driver nuget软件包。我试图返回集合中的文档列表，其中子文档字段等于我拥有的列表中包含的任何项目。理想情况下，对于dotnetcore 2.1的MongoDB.Driver nuget包，我需要使用C＃语法。

文档 { "_id" : "e29628a65e914c1e91b3fd9cbf6f2353", "Enabled" : true, "Name" : "Document123", "DisplayName" : "Some Document", "Description" : "Some Description", "Data" : [ "lastname", "email", "firstname", "zipcode" ], "Items" : [ { "_id" : "1", "Name" : "bob" }, { "_id" : "2", "Name" : "smith" } ] }

如果这是SQL，这就是我想要做的：

SELECT * FROM Document a, Item b WHERE a.Id = b.DocumentId AND b.Name IN ('bob', 'smith', 'alex')

以下是我们无法使用MongoDB驱动程序的情况：

string[] names = new [] { "bob", "smith", "alex" };
var document = new BsonDocument()
{
                new BsonElement("Items.Name", new BsonDocument()
                {
                    new BsonElement("$in", new BsonArray(names))
                })
            };
var itemsQuery = collection
                .Aggregate()
                .Match(document)
                ;

            var items = itemsQuery.ToList();

谢谢。

Answer 1

两个初始说明：

a）您的查询应在开始时包括一个$match阶段，以加快处理速度。两次$match可能有点奇怪，但是对于大量的文档，您会看到很大的不同，因为在$unwind阶段最终得到的文档要少得多。

b）您可以使用更少的代码编写基于字符串的查询，如下所示：

var itemsQuery = collection
    .Aggregate()
    .Unwind(document => document.Items)
    .Match("{ 'Name' : 'Document123', 'Items.Name' : { $in: [ '" + string.Join("', '", names) + "' ] } }");

但是您可以使用一种类型安全的版本（例如“不使用字符串或BsonDocument”）来编写所有这些代码，如下所示：

/// <summary>
/// This would be just to avoid having to create two almost identical types which, however, could be done as well if you don't like abstract base types
/// </summary>
public abstract class DocumentBase
{
    public string Id { get; set; }
    public string Name { get; set; }
    // this is where all other fields would go like "Enabled", "DisplayName", etc...
}

/// <summary>
/// Represents the <see cref="DocumentBase"/> type but with an unwound <see cref="Items"/> property which is actually a single <see cref="Item"/>,
/// </summary>
public class UnwoundDocument : DocumentBase
{
    public Item Items { get; set; }
}

/// <summary>
/// This is the real "Document" type with a <see cref="List{Item}"/> property called <see cref="Items"/>.
/// </summary>
public class Document : DocumentBase
{
    public List<Item> Items { get; set; }
}

/// <summary>
/// This would hold all properties of an Item - I've dropped the "Id" property since it's not needed for this sample
/// </summary>
public class Item
{
    public string Name { get; set; }
}

使用这些类型后，您可以运行以下代码：

public class Program
{
    static void Main(string[] args)
    {
        var collection = new MongoClient().GetDatabase("just_a_test").GetCollection<Document>("Document");
        // clear out all existing documents to allow for multiple runs of this sample app
        collection.DeleteMany(FilterDefinition<Document>.Empty);

        // insert our test document
        collection.InsertOne(new Document { Id = "some id", Name = "Document123", Items = new List<Item> { new Item { Name = "bob" }, new Item { Name = "smith" } } });

        // create a bunch of filters
        var namesToSearchFor = new List<string> { "bob", "smith", "alex" };
        Expression<Func<Item, bool>> itemFilter = item => namesToSearchFor.Contains(item.Name);
        FilterDefinitionBuilder<Document> fdb = Builders<Document>.Filter;
        FilterDefinition<Document> documentFilter = fdb.Eq(f => f.Name, "Document123") & fdb.ElemMatch(f => f.Items, itemFilter);

        // construct the aggregation pipeline
        IAggregateFluent<UnwoundDocument> pipeline = collection
            .Aggregate()
            .Match(documentFilter) // filter first for performance reasons (technically not needed)
            .Unwind(document => document.Items) // flatten the "Items" array
            .As(BsonSerializer.SerializerRegistry.GetSerializer<UnwoundDocument>()) // this is to tell the driver that the resulting document will look like our "UnwoundDocument" type
            .Match(d => namesToSearchFor.Contains(d.Items.Name)); // just so we can filter again and use the result in a nicely type-safe manner

        // just print out all results for demo purposes
        foreach (var result in pipeline.ToList())
        {
            Console.WriteLine(result.ToJson());
        }
    }
}

Answer 2

事实证明，此后我们不得不“放松”并运行匹配查询。这是对我们有用的代码。

        var collection = GetCollection<Document>();

        var document = new BsonDocument()
        {
            new BsonElement("Name", "Document123"),
            new BsonElement("Items.Name", new BsonDocument()
            {
                new BsonElement("$in", new BsonArray(new [] { "bob", "smith", "alex"}))
            })
        };

        var itemsQuery = collection
            .Aggregate()
            .Unwind(d => d.Items)
            .Match(document)
            ;

        var items = itemsQuery.ToList();

获取listOfStrings中subDocument.value的所有项目

2 个答案: