How to use $facet in C# Mongo Driver for following query?

Question

I would like to create an Aggregation on my data to get the total number of projects with specific tags for a collection of projects in my .Net application.

let type = 1
let dataPipeline = [];
dataPipeline = dataPipeline.concat([{
    "$match": {
      $and: [{
          "basicDetails.isDeleted": 0
        },
        {
          "basicDetails.type": type
        }
      ]
    },
  },
  {
    "$lookup": {
      from: "ProjectStatusTheme",
      localField: "id",
      foreignField: "basicDetails.status.id",
      as: "statusColorMapping"
    }
  },
  {
    "$facet": {
      "totalProjectsCount": [{
        "$group": {
          "_id": {
            "Status": {
              "id": -1,
              "name": "Total Projects",
            },
            "Color": {
              "$arrayElemAt": ["$statusColorMapping.color", {
                "$indexOfArray": ["$statusColorMapping.id", -1]
              }]
            },
          },
          "count": {
            "$sum": 1
          }
        }
      }],
      "countByStatus": [{
          "$group": {
            "_id": {
              "Status": "$basicDetails.status",
              "Color": {
                "$arrayElemAt": ["$statusColorMapping.color", {
                  "$indexOfArray": ["$statusColorMapping.id", "$basicDetails.status.id"]
                }]
              }
            },
            "count": {
              "$sum": 1
            },
          }
        },
        {
          $sort: {
            _id: 1
          }
        }
      ]
    }
  }
]);

I want to run the above query in .Net using the Aggregate Framework in MongoDB C# driver. I am able to run the match and lookup in .net as follows:

var match1 = new BsonDocument {
  {
    "$match",
    new BsonDocument {
      {
        "basicDetails.isDeleted",
        0
      }, {
        "basicDetails.type",
        Int16.Parse(type)
      }
    }
  }
};

var lookup1 = new BsonDocument {
  {
    "$lookup",
    new BsonDocument {
      {
        "from",
        "ProjectStatusTheme"
      }, {
        "localField",
        "id"
      }, {
        "foreignField",
        "basicDetails.status.id"
      }, {
        "as",
        "statusColorMapping"
      }
    }
  }
};

var pipeline = new [] {
  match1,
  lookup1
};

var result2 = projectsCollection.Aggregate < BsonDocument > (pipeline);

However, I am unable to convert $facet to the .NET C# Driver for Mongo. How can I do this using the .NET C# driver?

user_9492730 · Answer

You can use any valid BsonDocument stage via: BsonDocument.Parse("valid_bson_document_string"), so in your case it will be:

var pipeline = new [] {
  match1,
  lookup1,
  BsonDocument.Parse("facet_stage")
};
var result = coll.Aggregate(pipeline);

also, you may find examples of how to configure typed(and other) facet stages here

How to use $facet in C# Mongo Driver for following query?

1 Answers