Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p><strong>EDIT:</strong> To address the additional question from the comments:</p> <pre><code>static void TakesDog(Dog theDog) { ... } static void TakesBulldog(Bulldog theBulldog) { ... } static void TakesObject(object theObject) { ... } static void Main() { //Given these declarations... object dog = new BullDog(); Dog dog2 = new BullDog(); BullDog dog3 = new BullDog(); //These calls will work because a BullDog is a Dog: TakesDog(dog2); TakesDog(dog3); //this call will work because a Bulldog is a Bulldog: TakesBulldog(dog3); //and these calls will ALL work because all Dogs are Objects: TakesObject(dog); TakesObject(dog2); TakesObject(dog3); //However, these calls will fail because an Object or Dog is not //necessarily a Bulldog, //EVEN THOUGH our current dog and dog2 are indeed references to Bulldogs: TakesBulldog(dog); TakesBulldog(dog2); //An explicit conversion is necessary to make the above calls work: TakesBulldog(dog2 as Bulldog); //works given the current reference TakesBulldog((Bulldog)dog2); //works given the current reference TakesBulldog(dog as Bulldog); //ditto TakesBulldog((Bulldog)dog); //ditto //but if we change the value of dog2 to some other dog: dog2 = new Labrador(); //the above calls now fail: TakesBulldog(dog2 as Bulldog); //passes null into the method TakesBulldog((Bulldog)dog2); //throws InvalidCastException //you can avoid problems by checking the true type: if(dog2 is Bulldog) //interrogates the type of the referenced object TakesBulldog((Bulldog)dog2); //works else TakesDog(dog2); //general fallback case //Object is similar but even more basic: dog = "I'm a dog"; //now dog is a System.String //this call still works: TakesObject(dog); //but these will fail: TakesDog(dog); TakesBulldog(dog); } </code></pre> <p>One last thing to understand:</p> <pre><code>//given these declarations: object dog = new BullDog(); BullDog dog2 = new BullDog(); //even though dog is a BullDog, attempting to call BullDog-specific //members (methods, properties, fields) will fail: dog.Drool(); //you may only call members as specific as the object type of the //variable holding the reference: dog.ToString(); //defined by Object. If you've overridden it in Dog or BullDog, //you'll get that implementation dog2.Drool(); //works because we know from the variable that dog2 is a BullDog. </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POWhat is the difference between base reference type vs derived reference type
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USKeithS
    1. USKeithS
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POWhat is the difference between base reference type vs derived reference type
      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. CO+1 for a very thorough-looking example.
      singulars
      1. PO
      1. USShibumi
    2. COCan I rephrase the question again? What's diff between object a3 = new BullDog(); and BullDog a3 = new BullDog();
      singulars
      1. PO
      1. USom471987
 

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