50 lines
3.3 KiB
Markdown
50 lines
3.3 KiB
Markdown
# AI Context: Dynamic Query & Low-Code Engine
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## 1. Project Overview
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This project explores two distinct approaches for building a "Low-Code" style backend that supports dynamic field selection, complex filtering, and deep graph traversal without writing boilerplate code.
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## 2. Core Architectures
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### A. Hibernate/JPA Strategy (Runtime Dynamic)
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* **Goal**: Fully dynamic query construction at runtime.
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* **Key Components**:
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* `BaseRepository<T, ID>`: Extends `JpaRepository` & `JpaSpecificationExecutor`.
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* `BaseController<T>`: Provides generic `/list` endpoint.
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* `GenericSpecification`: Converts Map params to JPA Predicates.
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* Supports exact match (default).
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* Supports LIKE match via wildcard `*` (e.g., `name=John*`).
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* `Squiggly`: Used for dynamic JSON field projection (Graph-trimming) *after* DB fetch.
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* **Pros**: Zero code generation, extremely flexible, standard JPA ecosystem.
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* **Cons**: "N+1" issues if not careful (Entity Graph needed for optimization), limited by JPA's performance on complex joins.
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### B. MyBatis XML Generation Strategy (Compile/Runtime Generation)
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* **Goal**: Generate optimized, static-like SQL/XML artifacts for high performance and complex mapping.
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* **Key Components**:
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* `MyBatisGeneratorUtils`: The core engine.
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* **Mechanism**:
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1. **ResultMap Generation**:
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* Generates standard `<resultMap>` for each involved Entity.
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* Uses `columnPrefix` (e.g., `author$`, `books$`) to link nested associations/collections recursively.
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* This allows infinite recursion (Book -> Author -> Book) using the same set of ResultMaps.
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2. **SQL Generation**:
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* Builds a Join Tree based on requested fields (e.g., `["title", "author.books.title"]`).
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* Generates `LEFT JOIN`s automatically.
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* **Smart Alias Strategy**:
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* Table Alias: Full path (e.g., `book$author$books`) to avoid collisions.
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* Column Alias: `path$ColumnName` (e.g., `author$books$publish_month`).
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* **Crucial**: The last part of the alias MUST be the DB Column Name (not Java Field Name) to match `<result column="...">` during prefix stripping.
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3. **One-To-Many Handling**:
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* Detects `@OneToMany(mappedBy=...)` to generate correct `ON parent.id = child.parent_id` join condition.
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* **Forced ID Projection**: Automatically selects `id` columns for all nodes to ensure correct MyBatis collection folding.
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* **Pros**: High performance (single SQL), solves N+1, precise column selection.
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* **Cons**: Requires generation step (or runtime string manipulation), more complex engine logic.
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## 3. Key Files & Locations
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* `com.example.demo.util.MyBatisGeneratorUtils`: The "Brain" of the MyBatis strategy.
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* `com.example.demo.repository.GenericSpecification`: The "Brain" of the JPA strategy.
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* `com.example.demo.controller.BaseController`: The generic entry point.
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## 4. Current Status
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* JPA Strategy: Fully functional. Read operations support wildcard search and dynamic projection. Write operations support cascading creation and deep-merge patching.
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* MyBatis Strategy: Engine is complete and tested (`MyBatisGeneratorUtilsTest`). Capable of generating full valid XML with recursive mappings and List support. Integration into Controller is the next logical step.
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