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c#mongodb-querymongodb-.net-driverpocovar
Brian Var
Brian Var

Reputation: 6227

How to reference a 'var' from one method in another?

I know that a var is only in scope within it's method. But I've came across the situation where the collection 'var' from a database connection method, needs to be accessed in a subsequent Query() method in order to make a query.

The specific error is: The name collection doesn't exist in the current context

I've been referencing the MongoDB C# driver docs in order to set up the connection and the query and all seems correct besides this issue.

Does anyone know how I can restructure my code to resolve the error?

My two methods are specified as follows in an OrderRespository class, that makes database connections and queries:

//Method to create MongoDB Orders connection and get handle on collections
    public static bool CreateConnection()
    {

        var client = new MongoClient(connectionString);

        try
        {
          var database = client.GetDatabase("orders");
          //Get a handle on the customers collection:
          var collection = database.GetCollection<BsonDocument>("customers");
        }
        catch(MongoConnectionException)
        { 
            return false; 
        } 

        return true; 
    }



    //Method to test query on database documents
    public async static Task<List<Customer>> FindCustomers()
    {
        var documents =  await collection.Find(new BsonDocument()).ToListAsync();
        List<Customer> customerList = await documents.ToListAsync();

        return await documents.ToListAsync();

    }

And this is the customer Model POCO class that models the collection fields:

    public class Customer
    {
        /// <summary>
        /// This attribute is used to map the Id property to the ObjectId in the collection
        /// </summary>
        [BsonId]
        public ObjectId Id { get; set; }

        [BsonElement("firstName")]
        public string firstName { get; set; }

        [BsonElement("lastName")]
        public string lastName { get; set; }

        [BsonElement("email")]
        public string Email { get; set; }

    }

Upvotes: 0

Views: 103

Answers (1)

Servy
Servy

Reputation: 203837

CreateConnection should return the collection that it's creating so that the person creating the connection can actually use it:

//Consider renaming this method; you're really here to get the customers,
//not create a connection
public static YourCollectionType<BsonDocument> CreateConnection()
{
    var client = new MongoClient(connectionString);
    var database = client.GetDatabase("orders");
    //Get a handle on the customers collection:
    return database.GetCollection<BsonDocument>("customers");
}

FindCustomers can then accept the collection as a parameter:

public async static Task<List<Customer>> FindCustomers(
    YourCollectionType<BsonDocument> collection)
{
    var documents =  await collection.Find(new BsonDocument()).ToListAsync();
    List<Customer> customerList = await documents.ToListAsync();

    return await documents.ToListAsync();
}

You can then use CreateConnection to create the documents that you search through:

var customers = FindCustomers(CreateConnection());

If FindCustomers is something that would only ever make sense to use with a collection created by CreateConnection and you won't ever use the created object for anything else, then you could have FindCustomer call CreateConnection directly, but odds are those conditions won't apply.

Upvotes: 3

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