Linq Optimization Patterns

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

Anti-Patterns

Decision Tree

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:

# 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

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

Related Skills

• efcore-patterns - Entity configuration, migrations
• abp-framework-patterns - Repository patterns
• dotnet-async-patterns - Async/await correctness