PART IV · BACKEND

Validation

Checking whether incoming data follows required rules before it is processed.

01

What is it?

Validation checks whether data is acceptable before the system continues processing it.

Validation checks whether the input is valid.

02

Think of it like...

Think of a security checkpoint.

Before data enters the main process, it must pass the required checks.

Input
Validation
Valid / Invalid
03

What does it do?

Validation can check:

Required Fields

Is a value present when it must be?

Data Types

Is the value a number, text, boolean, or other expected type?

Allowed Values

Does it match one of the accepted choices?

Number Ranges

Is a number within the permitted limits?

Formats

Does it follow a required pattern, such as an email or date?

Business Constraints

Does it meet a rule required by the system?

04

Where is it used?

Validation is used in:

API Requests

Check data received by an endpoint.

Forms

Give users feedback before submission.

Backend Services

Protect processing from invalid input.

Data Imports

Check rows before they enter the system.

Business Workflows

Confirm each step has acceptable data.

Database Operations

Keep stored data within required rules.

05

Example

Order Request

Input

{
  "quantity": -10
}

Rule / Result

Rule:
quantity must be greater than 0

Result:
Validation Failed
06

How it connects

Request
Validation
Business Logic
Database

If invalid: Request → Validation → Error Response

07

Do Not Confuse

Validation

Checks whether data is acceptable.

Business Logic

Decides what the business operation should do.

Validation checks the input.
Business logic decides the action.

08

Topic Glossary

ENGLISH TERM中文SIMPLE ENGLISH中文小白理解
Validation校验Checking whether data follows required rules.在系统继续处理前检查输入数据是否符合要求。
Required Field必填字段A field that must contain a value.必须填写或传入数据的字段。
Data Type数据类型The kind of value a field accepts.字段允许接收的值类型，例如数字或文本。
Constraint约束A rule that limits allowed data.用来限制哪些数据可以被接受的规则。
Invalid Data无效数据Data that does not meet the rules.不符合系统规定的数据。
Validation Error校验错误An error returned when data fails validation.输入数据没有通过校验时返回的错误。
09

What to Remember

Validation checks data before processing.

Invalid input should be rejected clearly.

Validation protects business logic and data quality.

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