Category Archives: Root

Proxy Pattern

May 6, 2024 Sayed Leave a comment

Proxy Pattern:

“Proxy is a structural design pattern that lets you provide a substitute or placeholder for another object. A proxy controls access to the original object, allowing you to perform something either before or after the request gets through to the original object.”

“A credit card is a proxy for a bank account, which is a proxy for a bundle of cash. Both implement the same interface: they can be used for making a payment. A consumer feels great because there’s no need to carry loads of cash around. A shop owner is also happy since the income from a transaction gets added electronically to the shop’s bank account without the risk of losing the deposit or getting robbed on the way to the bank.”

Click on the images to see them clearly.

“In the above UML class diagram, the Proxy class implements the Subject interface so that it can act as substitute for Subject objects. It maintains a reference (realSubject) to the substituted object (RealSubject) so that it can forward requests to it (realSubject.operation()).”

UML Class Diagram

https://refactoring.guru/design-patterns/proxy

https://en.wikipedia.org/wiki/Proxy_pattern

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Java: Facade Design Pattern

May 6, 2024 Sayed Leave a comment

Façade Pattern

“Facade is a structural design pattern that provides a simplified interface to a library, a framework, or any other complex set of classes.”

“When you call a shop to place a phone order, an operator is your facade to all services and departments of the shop. The operator provides you with a simple voice interface to the ordering system, payment gateways, and various delivery services.”

For a clear view, click on the images (images are from Wikipedia)

Ref: https://refactoring.guru/design-patterns/facade

https://en.wikipedia.org/wiki/Facade_pattern

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Java : Decorator Design pattern

May 6, 2024 Sayed Leave a comment

Decorator Design pattern:

Decorator is a structural design pattern that lets you attach new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors.

Example:

Assume: A notifier class/object can send only email messages. But the application at a later time may want to use text/SMS, FB, or similar messages. With decorator pattern: decorate the Notifier class with other behaviours such as send SMS, send fb message, send twitter message (i.e. may create additional classes/objects (create link to original notifier class with interfaces/inheritance and aggregations/compositions) ). Then the client can use the original notifier class/object but dynamically point to the other classes/objects and use the corresponding sendMessage() method/behaviour for SMS, Text, FB, Twitter or similar messaging/notification.

Note: Inheritance/subclasses can be a choice but they have limitations. Aggregations/Compositions/interfaces will be used for the purpose of Decorator pattern.

Note: “When does a simple wrapper become the real decorator? As I mentioned, the wrapper implements the same interface as the wrapped object. That’s why from the client’s perspective these objects are identical.”

Ref: https://refactoring.guru/design-patterns/decorator

https://en.wikipedia.org/wiki/Decorator_pattern

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Java Structural Design Patterns

May 6, 2024 Sayed Leave a comment

Adapter Design Patterns

Ref: A good read: https://refactoring.guru/design-patterns/adapter

Ref: Wikipedia

Ref: https://www.visual-paradigm.com/guide/uml-unified-modeling-language/uml-aggregation-vs-composition/

	Auto	manual
Definition
Reliability	More	Less
Reuse	Always	May be possible
Batch	Always	Not possible
Time Saving	faster	Time consuming
Invest	Tool	Human
Performance	Load/Stress Performance possible	Not Possible/Cumbersome
Programming	Sort of required	Not needed
Framework	Can be used	Not needed
Operating System	Easier	Cumbersome
Regression	Easier	Cumbersome

Database Design in Pictures

Learn Some Data Flow Diagram (DFD)

SQL Server: Dynamic SQL, Stored Procedure, Cursor, SQL Injection, and similar

MS SQL Server Dynamic SQl, T-SQL

Mostly:

Dynamic SQL

Stored Procedure

Trigger

Cursor

Function

Sayed Ahmed

What are the Most Important Most Used

Design ERD

Convert ERD to database

Normalization

Indexing

SQL

Stored Procedure

Dynamic SQL

These will come, not too frequent

Function, User Defined Data Types, Temporary Table

Trigger, Cursor

SSRS, SSIS, SSAS

ML in SQL Server (in advanced level)

May not be important initially

Today

More on

Dynamic SQL

Stored Procedure

Cursor

Basics of Stored Procedure

By this time, we are supposed to know

Although these topics will come back

In our discussion today

From Northwind Database

Write a dynamic SQL

That will Query the Products table and

Show all data

Ref:

Dynamic SQL

DECLARE @table NVARCHAR(128), @sql NVARCHAR(MAX);

SET @table = N'Products'

SET @sql = N'SELECT * FROM ' + @table;

EXEC sp_executesql @sql;

Convert the previous to a stored procedure

Using dynamic SQL to query from any table of Northwind Database Write a stored Procedure for it table name as the parameter

Create or ALTER Procedure [dbo].[usp_query] ( @table NVARCHAR(128)) AS BEGIN

Some Topics to Know and Understand to prepare for a DBMS related Job Interview

ACID

ACID: https://www.geeksforgeeks.org/acid-properties-in-dbms

Database Normalization

1NF: No repeating groups possible for a cell, PK identified, dependencies mapped

2NF: No Partial Dependence. Non key attributes must have to depend on the full key

3NF: No transitive dependency. non key attributes must have to depend on the primary key, not on any other attributes. if there is another candidate key, still that is in 3NF

BCNF: 3NF satisfied but multiple candidate key exist then BCNF required

4NF: Multivalued Dependency exist. Need to remove that.

5NF: Do not have Join dependency

4NF: Normalization

Fourth Normal Form

Multivalued Dependency exist

Attributes independent of each other but depends on the same attribute

No row should show multivalued dependency

Solution: usually break into multiple tables

Definition: Multivalued Dependency:

5NF: is already in 4NF. and if contains join dependency.

Remove join dependency, break into new tables, but lossless break

Table: lecturer, semester, course.

We cannot create semester without knowing other attributes.

Not in 5NF

Solution: usually break into multiple tables

Normalization

Normalization: Determinant

Read Misc.: PL/SQL, T-SQL

PL/SQL Tutorial:

Oracle vs SQL Server

Oracle Vs MS SQL Server

T-SQL vs PL/SQL:

Cursors, Triggers, Functions, Stored Procedures

An INSTEAD OF trigger

is an SQL trigger that is processed “instead of” an SQL UPDATE, DELETE or INSERT statement. Unlike SQL BEFORE and AFTER triggers, an INSTEAD OF trigger can be defined only on a view, not a table.

MS SQL Server
Dynamic SQl, T-SQL

What are the Most Important
Most Used

Using dynamic SQL to query from any table of Northwind Database

Write a stored Procedure for it
table name as the parameter

Create or ALTER Procedure [dbo].[usp_query] ( @table NVARCHAR(128))
AS
BEGIN

Some Topics to Know and Understand
to prepare
for a DBMS related Job Interview