c# Generic method with async delegate

Question

I have created this generic method:

/// <summary> /// Executes a list of items /// </summary> /// <param name="procedureName">The name of the procedure</param> /// <param name="parameters">List of oracle parameters</param> /// <param name="limit">The limit of the results to return</param> /// <param name="mapper">The oracle mapper method</param> /// <returns></returns> protected async Task<IEnumerable<T>> ListAsync<T>(string procedureName, IList<OracleParameter> parameters, int limit, Func<IDataReader, T> mapper) { // Create our list var models = new List<T>(); var counter = 0; // Get our reader and return our model using (var reader = await _oracleUnitOfWork.ExecuteReaderAsync(procedureName, parameters)) { // While we have rows and our counter while (reader.Read() && ((counter < limit || limit == 0) || limit == 0)) { // If we have a limit, increase our counter (this is first to stop 0 based index messing the amount of objects to return) if (limit > 0) counter++; // Get our item from the database models.Add(mapper(reader)); } } // Return our list return models; }

Which I can invoke like this:

return await ListAsync("IBPA_MANFCOMPLAINT.complaintSearch", parameters, yield, OracleMapper.Complaint.Map);

But I want to extend this a little. The Mapper just uses the IDataReader to assign the column values to the model properties. For stock instead of using this:

return await ListAsync("ibpa_stock.readRelatedLotstoLot", parameters, 0, OracleMapper.Stock.Map);

I want to do a get request, a bit like this:

return await ListAsync("ibpa_stock.readRelatedLotstoLot", parameters, 0, async (reader) => await GetAsync(reader["lotno"].ToString()));

What can I do to keep things DRY, but at the same time to allow that invocation?

Is the problem that you sometimes have an async method and sometimes not? And the type Func<IDataReader, T> can't accomodate both? — Horia Coman
– Horia Coman, Commented Jan 11, 2018 at 15:38
Note that I'd strongly suggest you not have a method like this in the first place. Rather than having a single method that executes a procedure, takes the first N values of the result, and then maps each value to something else, taking in all of the information to do all of those things, you should instead have a method that gets the results of a procedure. If someone wants the first N items, they can call a method to take the first N items (Take). If they want to map the items into something else, they can call a method to do that (Select). You're not getting anything out doing this. — Servy
– Servy, Commented Jan 11, 2018 at 16:03
Yeah I know this :D but unfortunately I have no control over the sprocs — r3plica
– r3plica, Commented Jan 11, 2018 at 16:42
@r3plica You don't need to change anything about the stored procedures to make such a change, you just need to remove this unhelpful method and call the method that does each thing that you want when you want to do a thing, rather than trying to do them all at once, given that doing so doesn't get you anything, and has its costs. — Servy
– Servy, Commented Jan 11, 2018 at 17:12

Servy · Accepted Answer · 2018-01-11 15:44:31Z

1

You'll need to have two overloads of the method, one that accepts a Func<IDataReader, T>, and one that accepts a Func<IDataReader, Task<T>>. The second one will need to await the method call when it invokes it, the former won't.

answered Jan 11, 2018 at 15:44

Servy

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2 Comments

r3plica Over a year ago

That sounds fine, but won't there be a lot of repeated code?

Servy Over a year ago

@r3plica There's only a handful of code in the whole method, even as it sits, half of which doesn't need to be there at all, so no, not really.

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c# Generic method with async delegate

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