Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Yes, it will throw an <code>ArgumentNullException</code>. I can think of two reasons for putting the extra checking in:</p> <ul> <li>If you later go back and change the method to do something before calling <code>subjects.Count()</code> and forget to put the check in at that point, you could end up with a side effect before the exception is thrown, which isn't nice.</li> <li>Currently, the stack trace will show <code>subjects.Count()</code> at the top, and probably with a message with the <code>source</code> parameter name. This could be confusing to the caller of <code>HasFive</code> who can see a <code>subjects</code> parameter name.</li> </ul> <p>EDIT: Just to save me having to write it yet again elsewhere:</p> <p>The call to <code>subjects.Count()</code> will throw an <code>ArgumentNullException</code>, <em>not</em> a <code>NullReferenceException</code>. <code>Count()</code> is another extension method here, and assuming the implementation in <code>System.Linq.Enumerable</code> is being used, that's documented (correctly) to throw an <code>ArgumentNullException</code>. Try it if you don't believe me.</p> <p>EDIT: Making this easier...</p> <p>If you do a lot of checks like this you may want to make it simpler to do so. I like the following extension method:</p> <pre><code>internal static void ThrowIfNull&lt;T&gt;(this T argument, string name) where T : class { if (argument == null) { throw new ArgumentNullException(name); } } </code></pre> <p>The example method in the question can then become:</p> <pre><code>public static bool HasFive&lt;T&gt;(this IEnumerable&lt;T&gt; subjects) { subjects.ThrowIfNull("subjects"); return subjects.Count() == 5; } </code></pre> <p>Another alternative would be to write a version which checked the value <em>and returned it</em> like this:</p> <pre><code>internal static T NullGuard&lt;T&gt;(this T argument, string name) where T : class { if (argument == null) { throw new ArgumentNullException(name); } return argument; } </code></pre> <p>You can then call it fluently:</p> <pre><code>public static bool HasFive&lt;T&gt;(this IEnumerable&lt;T&gt; subjects) { return subjects.NullGuard("subjects").Count() == 5; } </code></pre> <p>This is also helpful for copying parameters in constructors etc:</p> <pre><code>public Person(string name, int age) { this.name = name.NullGuard("name"); this.age = age; } </code></pre> <p>(You might want an overload without the argument name for places where it's not important.)</p>
    singulars
    1. This table or related slice is empty.
    1. POC#: Should I bother checking for null in this situation?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USJon Skeet
    1. USJon Skeet
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POC#: Should I bother checking for null in this situation?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COGood points. On point #2, what if I renamed my subjects parameter to source?
      singulars
      1. PO
      1. USSvish
    2. COIt will actually throw a System.NullReferenceException. Suggest you edit the post.
      singulars
      1. PO
      1. UScodeape
    3. CO@codeape: No it won't, because Count() is also an extension method. Suggest you try it :)
      singulars
      1. PO
      1. USJon Skeet
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload