AgentSkillsCN

linq-optimization-patterns

为 ABP 框架优化 LINQ 与 EF Core 查询，预防 N+1 问题、实现提前加载、进行投影运算、实施分页处理。

SKILL.md
--- frontmatter
name: linq-optimization-patterns
description: "LINQ and EF Core query optimization for ABP Framework. N+1 prevention, eager loading, projections, pagination."
layer: 2
tech_stack: [dotnet, csharp, efcore, postgresql]
topics: [query-optimization, n-plus-one, eager-loading, projections, performance]
depends_on: []
complements: [efcore-patterns, abp-framework-patterns]
keywords: [Include, ThenInclude, Select, AsNoTracking, AsSplitQuery, WhereIf, N+1, CountAsync]

LINQ Optimization Patterns

Optimize LINQ queries and prevent performance anti-patterns in EF Core/ABP applications.

Summary

This skill covers efficient data access patterns for Entity Framework Core in ABP Framework applications. Focus areas: N+1 prevention, pagination, projections, and batch loading.

When to use: Reviewing queries, fixing slow endpoints, implementing list APIs.

Concepts

ConceptDescriptionDetails
Eager LoadingLoad related entities in single query via JOIN[patterns/eager-loading.md]
ProjectionTransform to DTO at database level[patterns/projection.md]
Batch LoadingLoad related data for multiple parents in one query[patterns/batch-loading.md]
PaginationEfficient paging with count optimization[patterns/pagination.md]

Anti-Patterns

Anti-PatternSeverityDetectImpactDetails
N+1 Query🔴 HIGHforeach.*await.*RepoN+1 DB calls[anti-patterns/n-plus-one.md]
Count After Pagination🔴 HIGHCount.*after.*ToListDouble query[anti-patterns/count-after-pagination.md]
Full Table Load🔴 HIGHGetListAsync() then filterMemory explosion[anti-patterns/full-table-load.md]
In-Memory Join🔴 HIGHMultiple ToListAsyncCartesian in memory[anti-patterns/in-memory-join.md]

Decision Tree

code
Need related data for display?
├─ Single entity ──────────► Include()        → [patterns/eager-loading.md]
├─ List of entities ───────► Batch load       → [patterns/batch-loading.md]
└─ Only specific fields ───► Projection       → [patterns/projection.md]

Need paginated list with count?
└─ Always count FIRST ─────► CountAsync()     → [patterns/pagination.md]

Loading data then filtering?
├─ Filter in query ────────► WhereIf()        → ✅ Correct
└─ Filter after ToList ────► ❌ Anti-pattern  → [anti-patterns/full-table-load.md]

Quick Detection

Run these to find issues in your codebase:

bash
# N+1: Query inside loop
grep -rn "foreach.*await.*Repository\|for.*await.*GetAsync" src/

# Count after pagination
grep -rn "\.Count().*ToList\|ToList.*\.Count()" src/

# Full table load
grep -rn "GetListAsync()" src/ | grep -v "Where\|Any\|First"

# In-memory filtering
grep -rn "ToListAsync().*\.Where\|GetListAsync.*\.Where" src/

Rules

IDRuleRelated
R001Execute CountAsync() before Skip/Take[anti-patterns/count-after-pagination.md]
R002Apply Where clauses before ToListAsync()[anti-patterns/full-table-load.md]
R003Load related entities via Include or batch, not in loops[anti-patterns/n-plus-one.md]
R004Use Select() projection for DTO returns[patterns/projection.md]
R005Use AsNoTracking() for read-only queries[patterns/projection.md]
R006Use AsSplitQuery() for multiple collection includes[patterns/eager-loading.md]

Checklist

Review checklist for LINQ queries:

  • • No foreach/for with await repository calls inside
  • • CountAsync() executed before Skip/Take
  • • No GetListAsync() followed by .Where() in memory
  • • No FirstOrDefault inside Select projections
  • • Related data loaded via Include or batch query
  • • Select() projection used for DTO returns
  • • AsNoTracking() used for read-only queries
  • • Multiple collection includes use AsSplitQuery()

Integration Points

This skill is used by:

  • •abp-code-reviewer: Query performance validation
  • •abp-developer: Efficient data access implementation
  • •debugger: Performance issue diagnosis

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