8/27/2021
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  1. Sequence Diagram Delete Object In C
  2. Sequence Diagram Delete Object In Html
  3. Sequence Diagram Delete Object
  4. Sequence Diagram Delete Objects

Collaborations and Components

Object Creation and Deletion. This is a sequence diagram example that shows object creation and deletion. Creation: arrow with 'new' written above it – notice that an object created after the start of the scenario appears lower than the others. Deletion: an X at bottom of object's lifeline – Java doesn't explicitly delete objects; they fall out of scope and are garbage-collected. The Sequence Diagram models the collaboration of objects based on a time sequence. It shows how the objects interact with others in a particular scenario of a use case. With the advanced visual modeling capability, you can create complex sequence diagram in few clicks.

A collaboration is a group of classes that work together to implement a component.

A collaboration instance is a group of objects that work together to implement a component instance.

A collaboration instance is just the runtime instantiation of a collaboration.

Components can be software components, hardware components, or business components.

The structure of a collaboration is given by a class diagram. The structure of a collaboration instance is given by an object diagram.

The interaction between the members of a collaboration can be given by a sequence role diagram or by a collaboration role diagram.

The interaction between the members of a collaboration instance can be given by a sequence diagram or a collaboration diagram.

I find Sequence/Sequence Role diagrams easier to understand than Collaboration/Collaboration Role diagrams and more fun to draw. Therefore I will only cover the former.

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Sequence Diagram Elements

Objects, Roles, and Lifelines

Sequence diagrams and sequence role diagrams are identical except that in a sequence diagram collaborators are objects while in a sequence role diagram collaborators are roles.

A role is sort of like an abstract or generic object. Different concrete objects can be plugged into a role.

A lifeline dangles under a role or object. This represents the lifetime of the role or object. Time is assumed to flow downward.

Here are some examples of roles:

Here are examples of objects:

Use roles when modeling a collaboration. Use objects when modeling a collaboration instance.

Stimulus/Message

Objects send stimuli to one another, while roles send messages. Other than that, the distinction seems unimportant.

There are five types of messages/stimuli: Call, Send, Return, Create, and Destroy. Objects/Roles can also send messages/stimuli to themselves. The following diagram shows all five types:

Sequence Diagram Delete Object

The sender begins by calling its own demo method. The yellow bar indicates the period of time that this method is running. The demo method creates a new instance of the ReceiverClass called receiver. At the end of the demo method the receiver will be destroyed.

Next, the sender calls the receiver's m1 method with inputs a1 and a2. This is a conditional call. It only is made if guard is true. The return value is stored in a variable called result. Alternatively, the returned result can be shown by the return message sent from the receiver back to the sender. Calling a method is an example of a synchronous message. The sender blocks until the receiver is finished processing the message and has returned a value or sent some sort of acknowledgement.

Next, the sender sends the message m2 with inputs a3 and a4 to the receiver. This message is sent again and again until the guard condition becomes false. Sent messages are asynchronous. The sender does not need to wait for a reply. Sending messages requires that the receiver has some sort of message queue where the messages can be stored until the receiver has time to process them. Once a message has been stored in a queue, the sender can go on to do other things.

Here is how this sequence diagram might be expressed in C++:

class SenderClass {
public:
void demo() {
ReceiverClass* receiver = new ReceiverClass();
if (guard) result = receiver->m1(a1, a2);
while(guard) receiver->msgQueue << m2(a3, a4);
delete receiver;
}
// etc.
};

Example

The scenario:

A client selects a menu item on a control panel. In response, the control panel creates a command and asks a command processor to execute it. The command processor asks the command to execute itself, stores the result, deletes the command, then returns the result to the control panel to be displayed.

The sequence diagram:

Combined Fragments and Interaction Operands

Fragments of sequence diagrams can be identified and qualified.

Options (One-Way Conditionals)

An optional fragment is only executed if some guard condition is true:

Alternatives (Multi-Way Conditionals)

An alternative fragment provides several guarded alternative fragments (separated by interaction operands):

Loops

A loop allows a fragment to be repeated until some guard condition becomes false:

Break

A break allows an enclosing loop to be escaped when some guard becomes true:

Parallel

A parallel fragment allows multiple interactions to run in parallel:

Other Fragment Types

Strict

Assert

Consider

Ignore

Region

Neg

Frames

A frame provides a way to encapsulate a sequence diagram.

A frame can be referenced in another sequence diagram:

Examples

Protocols

Collaborations

Scenarios

Signals and Receptions

An auctioneer broadcasts a proposed price for an item to a crowded room of anxious bidders. When a bidder hears the proposal he decides to accept the price or not.

Sequence Diagram Delete Object In C

In an automated auction, how will the auctioneer broadcast the proposal? An object may have designated operations that should automatically be called if certain types of broadcast signals are received. These methods are called receptions. Signals are a special kind of class. The name of the reception usually matches the name of the signal. Receptions are shown in a separate compartment:

In a sequence diagram we can represent a signal as an asynchronous signal, and the reception as a reception invocation:

Summary: in this tutorial, you will learn how to use MySQL ON DELETE CASCADE referential action for a foreign key to delete data from multiple related tables.

In the previous tutorial, you learned how to delete data from multiple related tables using a single DELETE statement. However, MySQL provides a more effective way called ON DELETE CASCADE referential action for a foreign key that allows you to delete data from child tables automatically when you delete the data from the parent table.

MySQL ON DELETE CASCADE example

Sequence Diagram Delete Object In Html

Let’s take a look at an example of using MySQL ON DELETE CASCADE .

Suppose that we have two tables:buildings and rooms . In this database model, each building has one or many rooms. However, each room belongs to one only one building. A room would not exist without a building.

The relationship between the buildings and rooms tables is one-to-many (1:N) as illustrated in the following database diagram:

When you delete a row from the buildings table, you also want to delete all rows in the rooms table that references to the row in the buildings table. For example, when you delete a row with building no. 2 in the buildings table as the following query:

You also want the rows in the rooms table that refers to building number 2 will be also removed.

Sequence Diagram Delete Object

The following are steps that demonstrate how the ON DELETE CASCADE referential action works.

Step 1. Create the buildings table:

Step 2. Create the rooms table:

Notice that the ON DELETE CASCADE clause at the end of the foreign key constraint definition.

Step 3. Insert rows into the buildings table:

Step 4. Query data from the buildings table:

We have two rows in the buildings table.

Step 5. Insert rows into the rooms table:

Sequence Diagram Delete Objects

Step 6. Query data from the rooms table:

We have three rooms that belong to building no 1 and two rooms that belong to the building no 2.

Step 7. Delete the building with building no. 2:

Step 8. Query data from rooms table:

As you can see, all the rows that reference to building_no 2 were automatically deleted.

Notice that ON DELETE CASCADE works only with tables with the storage engines that support foreign keys e.g., InnoDB.

Some table types do not support foreign keys such as MyISAM so you should choose appropriate storage engines for the tables that you plan to use the MySQL ON DELETE CASCADE referential action.

Tips to find tables affected by MySQL ON DELETE CASCADE action

Sometimes, it is useful to know which table is affected by the ON DELETE CASCADE referential action when you delete data from a table. You can query this data from the referential_constraints in the information_schema database as follows:

For example, to find tables that associated with the buildings table with the CASCADE deletion rule in the classicmodels database, you use the following query:

In this tutorial, you have learned how to use the MySQL ON DELETE CASCADE referential action for a foreign key to delete data automatically from the child tables when you delete data from the parent table.