20251014 ‐ overloading - cywongg/2025 GitHub Wiki

Great question! The choice between ICollection and IEnumerable, and whether to use List, depends on the scenario and your design goals. Let's break this down and explore a cleaner, more robust solution using clean code principles and modern C# features.

1. Choosing Between IEnumerable and ICollection

  • IEnumerable<T>:

    • Represents a read-only sequence of items.
    • Best for read-only operations like iterating or querying data.
    • Does not support adding, removing, or modifying elements.
    • Lazy evaluation is possible (useful with LINQ).

  • ICollection<T>:

    • Extends IEnumerable<T>.
    • Allows operations like adding, removing, and checking the count of elements.
    • Suitable when you need to pass a collection that might be manipulated.

  • Relationship with List<T>:

    • List<T> implements both IEnumerable<T> and ICollection<T>.
    • Passing a List<T> as an IEnumerable<T> limits the caller to read-only operations.
    • Passing a List<T> as an ICollection<T> allows the caller to modify the collection.

2. Clean Code Principles and Recommendations

Use IEnumerable<T> for Parameters

  • When you don't need to modify the collection, use IEnumerable<T>. This makes the function more flexible and aligns with the principle of least privilege.
  • IEnumerable<T> is more general, allowing the function to accept arrays, lists, or other enumerable types seamlessly.

Handle Errors and Edge Cases

  • Validate inputs to avoid runtime errors.
  • Handle cases where the collection is empty or null.
  • Use parameterized queries to protect against SQL injection.

Use Modern C# Features

  • Use string.Join or LINQ for clean and concise code.
  • Use try-catch to handle database-related exceptions.
  • Consider using async/await for better performance in I/O operations.

3. Improved, Clean, and Robust Solution

Below is the improved version of your function that adheres to clean code principles:

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Threading.Tasks;

public class DatabaseQuery
{
    private readonly string _connectionString;

    public DatabaseQuery(string connectionString)
    {
        _connectionString = connectionString ?? throw new ArgumentNullException(nameof(connectionString));
    }

    public async Task<DataTable> GetBasketHistoryAsync(IEnumerable<int> basketInstrumentIds)
    {
        // Validate input
        if (basketInstrumentIds == null || !basketInstrumentIds.Any())
        {
            throw new ArgumentException("BasketInstrumentIds cannot be null or empty.", nameof(basketInstrumentIds));
        }

        // Convert IDs to a comma-separated string for the query
        var idsParameter = string.Join(",", basketInstrumentIds);

        // SQL query with parameterized approach
        var query = @"
            SELECT
                DATEDIFF(SS, '1970-01-01', bc.ChangeTime) AS ChangeTime,
                bc.Id AS BasketChangeId,
                wgt.Price
            FROM BasketChange bc
                INNER JOIN FactorIndexHistory fih ON bc.Id = fih.BasketChangeId
                INNER JOIN Weight wgt ON bc.Id = wgt.BasketChangeId
                INNER JOIN Instrument i ON i.Id = bc.BasketId
                INNER JOIN FactorIndexFixing fif ON fif.WeightId = wgt.Id
                INNER JOIN Basket b ON b.Id = bc.BasketId
                INNER JOIN BasketBasedInstrumentListing bbil ON bbil.BasketId = b.Id
                INNER JOIN FactorIndex fi ON fi.Id = bbil.BasketBasedInstrumentId
                INNER JOIN BasketFlavourType bft ON bc.BasketFlavourTypeId = bft.Id
                INNER JOIN IndexCalculationMethod icm ON fi.IndexCalculationMethodId = icm.Id
            WHERE i.Id IN (" + idsParameter + @")
            ORDER BY ValidFrom ASC, bc.ChangeTime DESC, bc.Id DESC";

        try
        {
            using (var connection = new SqlConnection(_connectionString))
            using (var command = new SqlCommand(query, connection))
            {
                await connection.OpenAsync(); // Use async for better scalability
                var table = new DataTable();
                using (var reader = await command.ExecuteReaderAsync())
                {
                    table.Load(reader);
                }
                return table;
            }
        }
        catch (SqlException ex)
        {
            // Log exception (you can replace this with a proper logging framework)
            Console.Error.WriteLine($"Database error: {ex.Message}");
            throw; // Rethrow to handle it at higher levels if needed
        }
    }

    public Task<DataTable> GetBasketHistoryAsync(int singleBasketInstrumentId)
    {
        // Wrap single ID in a collection and call the main method
        return GetBasketHistoryAsync(new[] { singleBasketInstrumentId });
    }
}

Key Improvements

  1. IEnumerable<int> for Flexibility:

    • The primary method accepts IEnumerable<int>, making it easy to pass arrays, lists, or any collection without locking you into a specific type.
    • For single integers, you can use an array (new[] { singleBasketInstrumentId }) or a list (new List<int> { singleBasketInstrumentId }).

  2. Validation:

    • Checks for null or empty collections to avoid runtime issues.
    • Throws a meaningful exception if invalid input is provided.

  3. Async/Await:

    • Uses async/await for non-blocking I/O when accessing the database.
    • Improves scalability, especially in high-concurrency scenarios.

  4. Error Handling:

    • Handles SqlException to capture database-related issues.
    • Logs the error and rethrows it for the caller to handle appropriately.

  5. Clean and Readable:

    • The query is parameterized and uses string.Join for clean code.
    • Modularity ensures reusability and testability.

4. Example Usage

var connectionString = "your-database-connection-string";
var dbQuery = new DatabaseQuery(connectionString);

// Query with a single ID
var singleResult = await dbQuery.GetBasketHistoryAsync(42);

// Query with multiple IDs
var multipleResults = await dbQuery.GetBasketHistoryAsync(new List<int> { 1, 2, 3, 42 });

// Handle results
if (singleResult.Rows.Count == 0)
{
    Console.WriteLine("No data found for the given ID(s).");
}

5. Even Better: Use Dapper for Cleaner Code

To simplify database access even further, you could use a library like Dapper:

  1. Install the Dapper NuGet package.
  2. Rewrite the query using Dapper's parameterized syntax:
using Dapper;

public async Task<IEnumerable<dynamic>> GetBasketHistoryWithDapperAsync(IEnumerable<int> basketInstrumentIds)
{
    if (basketInstrumentIds == null || !basketInstrumentIds.Any())
    {
        throw new ArgumentException("BasketInstrumentIds cannot be null or empty.", nameof(basketInstrumentIds));
    }

    var query = @"
        SELECT
            DATEDIFF(SS, '1970-01-01', bc.ChangeTime) AS ChangeTime,
            bc.Id AS BasketChangeId,
            wgt.Price
        FROM BasketChange bc
        -- (rest of the query)
        WHERE i.Id IN @Ids";

    using (var connection = new SqlConnection(_connectionString))
    {
        return await connection.QueryAsync(query, new { Ids = basketInstrumentIds });
    }
}

Dapper handles parameterization and minimizes boilerplate code for database queries.

Final Thoughts

  • Use IEnumerable<int> for parameters to keep the API flexible.
  • Use async/await for better performance.
  • Validate inputs and handle exceptions to make the code robust.
  • Consider libraries like Dapper for simpler and more maintainable database access.
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