7 gefährliche Fehler, die in C # /. NET leicht zu machen sind

1. Verstehe die verzögerte (faule) Ausführung nicht

[TestMethod]
[ExpectedException(typeof(ArgumentNullException))]
public void Ensure_Null_Exception_Is_Thrown()
{
   var result = RepeatString5Times(null);
}
[TestMethod]
[ExpectedException(typeof(InvalidOperationException))]
public void Ensure_Invalid_Operation_Exception_Is_Thrown()
{
   var result = RepeatString5Times("test");
   var firstItem = result.First();
}
private IEnumerable<string> RepeatString5Times(string toRepeat)
{
   if (toRepeat == null)
       throw new ArgumentNullException(nameof(toRepeat));
   for (int i = 0; i < 5; i++)
   {   
       if (i == 3)
            throw new InvalidOperationException("3 is a horrible number");
       yield return $"{toRepeat} - {i}";
   }
}

2. , Dictionary ,

var dict = new Dictionary<string, object>();       
dict.Add("first", new object());
dict.Add("second", new object());
dict.Remove("first");
dict.Add("third", new object());
foreach (var entry in dict)
{
    Console.WriteLine(entry.Key);
}

3. Flusssicherheit nicht berücksichtigen

var items = new List<int>();
var tasks = new List<Task>();
for (int i = 0; i < 5; i++)
{
   tasks.Add(Task.Run(() => {
       for (int k = 0; k < 10000; k++)
       {
           items.Add(i);
       }
   }));
}
Task.WaitAll(tasks.ToArray());
Console.WriteLine(items.Count);

28191
23536
44346
40007
40476

4. Missbrauch des verzögerten (verzögerten) Ladens in LINQ

using (var db = new DBEntities())
{
   var modules = db.Modules;
   foreach (var module in modules)
   {
       var moduleType = module.Results;
      //   
   }
}

using (var db = new DBEntities())
{
   var modules = db.Modules.Include(b => b.Results);
   foreach (var module in modules)
   {
       var moduleType = module.Results;
      //   
   }
}

5. Verstehen Sie nicht, wie LINQ to SQL / Entity Frameworks Abfragen übersetzt

var modules = from m in db.Modules
              select m.Name.Split(':')[1];

int modules = db.Modules.Sum(a => a.ID);

int modules = db.Modules.ToList().Sum(a => a.ID);

6. Falsche Rundung

Math.Round(2.25,1, MidpointRounding.AwayFromZero)

7. Schreckliche Klasse 'DBNull'

reader.GetString(0) ?? "NULL";

reader.GetString(0) != DBNull.Value ? reader.GetString(0) : "NULL";

Hinweis