如何查询创建视图所用管道？含MongoDB 3.6.4及.NET Driver 2.6.1方案

Hey there! Let's tackle your two questions about retrieving the pipeline used to create a MongoDB view:

1. Shell command for MongoDB 3.6.4 #

In MongoDB 3.6.4, all view definitions are stored in the system.views collection of your target database. To fetch the pipeline for a specific view, you can query this collection directly.

Here's the basic command to get the full view document (which includes the pipeline):

db.getCollection("system.views").find({ name: "your_view_name" })

If you want a cleaner output that only returns the pipeline (and excludes the default _id field), use this projection:

db.system.views.find(
    { name: "your_view_name" },
    { pipeline: 1, _id: 0 }
)

Just replace "your_view_name" with the actual name of your view. The returned pipeline array will list all the aggregation stages used when creating the view.

2. Can the .NET Driver 2.6.1 retrieve this pipeline? #

Yes, you absolutely can! Even though the 2.6.1 driver is a bit dated, it’s compatible with MongoDB 3.6.4 and supports querying the system.views collection (since views were introduced in MongoDB 3.4, which the 2.x driver family fully supports).

Here's a practical code example using BsonDocument (a straightforward approach for older driver versions):

using MongoDB.Bson;
using MongoDB.Driver;

var client = new MongoClient("your_connection_string");
var database = client.GetDatabase("your_database_name");
var systemViewsCollection = database.GetCollection<BsonDocument>("system.views");

// Filter to target your specific view
var filter = Builders<BsonDocument>.Filter.Eq("name", "your_view_name");
var viewDocument = systemViewsCollection.Find(filter).FirstOrDefault();

if (viewDocument != null && viewDocument.Contains("pipeline"))
{
    // Extract the pipeline as a BsonArray
    var pipeline = viewDocument["pipeline"].AsBsonArray;
    
    // You can iterate through stages or convert them to readable strings
    foreach (var stage in pipeline)
    {
        Console.WriteLine(stage.ToString());
    }
}

If you prefer strongly-typed objects, you could also create a class that maps to the system.views document structure, but using BsonDocument is the simplest way to get the job done with this driver version.

内容的提问来源于stack exchange，提问作者Hackworth