117 lines
2.6 KiB
Plaintext
117 lines
2.6 KiB
Plaintext
---
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title: Database Design
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description: MCD, MLD and MPD for MemeGoat.
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---
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## Conceptual Data Model (MCD)
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The MCD defines entities and their relationships.
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```mermaid
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erDiagram
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USER ||--o{ MEME : "creates"
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USER ||--o{ COMMENT : "writes"
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MEME ||--o{ COMMENT : "receives"
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MEME }o--o{ TAG : "has"
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USER {
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string username
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string email
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string password
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datetime created_at
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}
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MEME {
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string title
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string image_url
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datetime created_at
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}
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TAG {
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string name
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}
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COMMENT {
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string content
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datetime created_at
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}
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```
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## Logical Data Model (MLD)
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The MLD translates the MCD into tables with foreign keys.
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```mermaid
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erDiagram
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users ||--o{ memes : "user_id"
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users ||--o{ comments : "user_id"
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memes ||--o{ comments : "meme_id"
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memes ||--o{ meme_tags : "meme_id"
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tags ||--o{ meme_tags : "tag_id"
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users {
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uuid id PK
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varchar username
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varchar email
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text password_hash
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timestamp created_at
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}
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memes {
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uuid id PK
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varchar title
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text image_url
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uuid user_id FK
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timestamp created_at
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}
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tags {
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uuid id PK
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varchar name
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}
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meme_tags {
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uuid meme_id FK
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uuid tag_id FK
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}
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comments {
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uuid id PK
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text content
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uuid user_id FK
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uuid meme_id FK
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timestamp created_at
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}
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```
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## Physical Data Model (MPD)
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SQL implementation for PostgreSQL.
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```sql
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CREATE TABLE users (
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id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
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username VARCHAR(50) UNIQUE NOT NULL,
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email VARCHAR(255) UNIQUE NOT NULL,
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password_hash TEXT NOT NULL,
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created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
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);
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CREATE TABLE memes (
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id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
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title VARCHAR(255) NOT NULL,
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image_url TEXT NOT NULL,
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user_id UUID REFERENCES users(id) ON DELETE SET NULL,
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created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
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);
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CREATE TABLE tags (
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id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
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name VARCHAR(50) UNIQUE NOT NULL
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);
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CREATE TABLE meme_tags (
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meme_id UUID REFERENCES memes(id) ON DELETE CASCADE,
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tag_id UUID REFERENCES tags(id) ON DELETE CASCADE,
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PRIMARY KEY (meme_id, tag_id)
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);
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CREATE TABLE comments (
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id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
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content TEXT NOT NULL,
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user_id UUID REFERENCES users(id) ON DELETE SET NULL,
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meme_id UUID REFERENCES memes(id) ON DELETE CASCADE,
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created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP
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);
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```
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