SOLID Principles in PHP

This post is to provide an easy to understand idea about the implementation of one of the most “talked about” principles of Object Oriented Programming - SOLID principles. As a programmer, there might come a time when we are so consumed in finishing the task at hand that we forget the world around us. And in the very same world, somewhere lost are the programming principles that we read about and planned to use next time. So let’s try to look at the SOLID principles in one of the simplest way possible so that we can practice them while coding.

So let’s dig in to the SOLID principles at a glance.

1. Single Responsibility: A Class should be responsible for a single task.
2. Open-Close Principle: A Class should be open to extension and close to modification.
3. Liskov Substitution: A derived Class can be substituted at places where base Class is used.
4. Interface Segregation: Don’t make FAT Interfaces. i.e. Classes don’t have to override extra agreements that are not needed for that Class simply because it is there in interface.
5. Dependency Inversion: Depend on abstractions, not on concretions. Not only high level Classes but low level Classes also depend on the abstractions in order to decouple the code.

ENUM and SET Constraints

 ENUM and SET columns provide an efficient way to define columns that can contain only a given set of values. See Section 11.3.5, “The ENUM Type”, and Section 11.3.6, “The SET Type”.

Unless strict mode is disabled (not recommended, but see Section 5.1.11, “Server SQL Modes”), the definition of a ENUM or SET column acts as a constraint on values entered into the column. An error occurs for values that do not satisfy these conditions:

• An ENUM value must be one of those listed in the column definition, or the internal numeric equivalent thereof. The value cannot be the error value (that is, 0 or the empty string). For a column defined as ENUM('a','b','c'), values such as '', 'd', or 'ax' are invalid and are rejected.

• A SET value must be the empty string or a value consisting only of the values listed in the column definition separated by commas. For a column defined as SET('a','b','c'), values such as 'd' or 'a,b,c,d' are invalid and are rejected.

Errors for invalid values can be suppressed in strict mode if you use INSERT IGNORE or UPDATE IGNORE. In this case, a warning is generated rather than an error. For ENUM, the value is inserted as the error member (0). For SET, the value is inserted as given except that any invalid substrings are deleted. For example, 'a,x,b,y' results in a value of 'a,b'.

The ENUM Type

 An ENUM is a string object with a value chosen from a list of permitted values that are enumerated explicitly in the column specification at table creation time.

See Section 11.3.1, “String Data Type Syntax” for ENUM type syntax and length limits.

The ENUM type has these advantages:

• Compact data storage in situations where a column has a limited set of possible values. The strings you specify as input values are automatically encoded as numbers. See Section 11.7, “Data Type Storage Requirements” for storage requirements for the ENUM type.

• Readable queries and output. The numbers are translated back to the corresponding strings in query results.

and these potential issues to consider:

• If you make enumeration values that look like numbers, it is easy to mix up the literal values with their internal index numbers, as explained in Enumeration Limitations.

• Using ENUM columns in ORDER BY clauses requires extra care, as explained in Enumeration Sorting.

• Creating and Using ENUM Columns

• Index Values for Enumeration Literals

• Handling of Enumeration Literals

• Empty or NULL Enumeration Values

• Enumeration Sorting

• Enumeration Limitations