Ef Core Advanced Patterns

Entity Framework Core Advanced Patterns

Master EF Core patterns for building high-performance, maintainable data access layers with PostgreSQL.

When to Use This Skill

• Optimizing database query performance
• Eliminating N+1 query problems
• Managing change tracking efficiently
• Implementing bulk operations
• Handling concurrency conflicts
• Working with PostgreSQL-specific features
• Debugging slow EF Core queries
• Optimizing memory usage

Core Concepts

1. Change Tracking Optimization

No-Tracking Queries for Read-Only Operations:

// Bad: Unnecessary tracking overhead
public async Task<List<PatientDto>> GetPatientsAsync()
{
    var patients = await _dbContext.Patients.ToListAsync();
    return _mapper.Map<List<PatientDto>>(patients);
}

// Good: No tracking for read-only queries
public async Task<List<PatientDto>> GetPatientsAsync()
{
    var patients = await _dbContext.Patients
        .AsNoTracking()
        .ToListAsync();
    return _mapper.Map<List<PatientDto>>(patients);
}

// Best: Configure no-tracking at query level or globally
public class ClinicDbContext : AbpDbContext<ClinicDbContext>
{
    public ClinicDbContext(DbContextOptions<ClinicDbContext> options)
        : base(options)
    {
        // Global no-tracking (opt-in tracking when needed)
        ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
    }
}

Identity Resolution:

// NoTrackingWithIdentityResolution: Tracks for query duration only
var patients = await _dbContext.Patients
    .AsNoTrackingWithIdentityResolution()
    .Include(p => p.Appointments)
        .ThenInclude(a => a.Doctor)
    .ToListAsync();
// Ensures same entity instances are used within this query
// But not tracked after query completes

Change Tracker Management:

public async Task ProcessLargeBatchAsync()
{
    var patients = await _dbContext.Patients.ToListAsync();

    foreach (var patient in patients)
    {
        // Process patient
        patient.LastProcessedDate = DateTime.UtcNow;

        // Every 100 entities, save and clear tracker
        if (patients.IndexOf(patient) % 100 == 0)
        {
            await _dbContext.SaveChangesAsync();
            _dbContext.ChangeTracker.Clear(); // Free memory
        }
    }

    await _dbContext.SaveChangesAsync();
}

2. Loading Strategies

Eager Loading with Include:

// Basic Include
var appointments = await _dbContext.Appointments
    .Include(a => a.Patient)
    .Include(a => a.Doctor)
    .ToListAsync();

// ThenInclude for nested navigation
var appointments = await _dbContext.Appointments
    .Include(a => a.Patient)
        .ThenInclude(p => p.MedicalRecords)
    .Include(a => a.Doctor)
        .ThenInclude(d => d.Specializations)
    .ToListAsync();

// Filtered Include (EF Core 5+)
var doctors = await _dbContext.Doctors
    .Include(d => d.Appointments.Where(a => a.Status == AppointmentStatus.Scheduled))
    .ToListAsync();

// Multiple navigation properties
var patients = await _dbContext.Patients
    .Include(p => p.Appointments)
    .Include(p => p.MedicalRecords)
    .Include(p => p.PrimaryDoctor)
    .ToListAsync();

Explicit Loading:

// Load related entities on demand
var patient = await _dbContext.Patients
    .FirstOrDefaultAsync(p => p.Id == patientId);

// Explicitly load appointments
await _dbContext.Entry(patient)
    .Collection(p => p.Appointments)
    .LoadAsync();

// Explicitly load with filtering
await _dbContext.Entry(patient)
    .Collection(p => p.Appointments)
    .Query()
    .Where(a => a.AppointmentDate >= DateTime.Today)
    .LoadAsync();

// Load and count without loading all data
var appointmentCount = await _dbContext.Entry(patient)
    .Collection(p => p.Appointments)
    .Query()
    .CountAsync();

Lazy Loading (Use Sparingly):

// Enable lazy loading (requires proxies)
public class ClinicDbContext : AbpDbContext<ClinicDbContext>
{
    public ClinicDbContext(DbContextOptions<ClinicDbContext> options)
        : base(options)
    {
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseLazyLoadingProxies();
    }
}

// Virtual navigation properties enable lazy loading
public class Patient
{
    public virtual ICollection<Appointment> Appointments { get; set; }
    // WARNING: Can cause N+1 queries if not careful
}

3. Query Splitting

Avoid Cartesian Explosion:

// Bad: Single query with multiple includes causes cartesian explosion
var doctors = await _dbContext.Doctors
    .Include(d => d.Appointments)
    .Include(d => d.DoctorSchedules)
    .Include(d => d.Specializations)
    .ToListAsync();
// Results in: Doctors × Appointments × Schedules × Specializations rows

// Good: Split query to avoid cartesian product
var doctors = await _dbContext.Doctors
    .Include(d => d.Appointments)
    .Include(d => d.DoctorSchedules)
    .Include(d => d.Specializations)
    .AsSplitQuery()
    .ToListAsync();
// Executes 4 separate queries and combines results

Global Split Query Configuration:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder
        .UseNpgsql(connectionString)
        .UseQuerySplittingBehavior(QuerySplittingBehavior.SplitQuery);
}

4. Compiled Queries

Pre-compile Frequently Used Queries:

public class PatientQueries
{
    // Compiled query for better performance
    private static readonly Func<ClinicDbContext, Guid, Task<Patient>> _getPatientByIdQuery =
        EF.CompileAsyncQuery((ClinicDbContext context, Guid id) =>
            context.Patients
                .Include(p => p.PrimaryDoctor)
                .FirstOrDefault(p => p.Id == id));

    private static readonly Func<ClinicDbContext, string, Task<Patient>> _getPatientByEmailQuery =
        EF.CompileAsyncQuery((ClinicDbContext context, string email) =>
            context.Patients
                .FirstOrDefault(p => p.Email == email));

    public static Task<Patient> GetByIdAsync(ClinicDbContext context, Guid id)
        => _getPatientByIdQuery(context, id);

    public static Task<Patient> GetByEmailAsync(ClinicDbContext context, string email)
        => _getPatientByEmailQuery(context, email);
}

// Usage
var patient = await PatientQueries.GetByIdAsync(_dbContext, patientId);

5. Batch Operations (EF Core 7+)

ExecuteUpdate - Bulk Update Without Loading:

// Bad: Load all entities, update, save
var patients = await _dbContext.Patients
    .Where(p => p.IsActive == false)
    .ToListAsync();

foreach (var patient in patients)
{
    patient.Status = PatientStatus.Inactive;
}

await _dbContext.SaveChangesAsync();

// Good: Bulk update in single SQL statement
await _dbContext.Patients
    .Where(p => p.IsActive == false)
    .ExecuteUpdateAsync(setters => setters
        .SetProperty(p => p.Status, PatientStatus.Inactive)
        .SetProperty(p => p.LastModifiedDate, DateTime.UtcNow));

// Update with expression
await _dbContext.Appointments
    .Where(a => a.AppointmentDate < DateTime.Today && a.Status == AppointmentStatus.Scheduled)
    .ExecuteUpdateAsync(setters => setters
        .SetProperty(a => a.Status, AppointmentStatus.Expired)
        .SetProperty(a => a.Notes, a => a.Notes + " [Auto-expired]"));

ExecuteDelete - Bulk Delete Without Loading:

// Bad: Load and delete
var oldAppointments = await _dbContext.Appointments
    .Where(a => a.AppointmentDate < DateTime.Today.AddYears(-2))
    .ToListAsync();

_dbContext.Appointments.RemoveRange(oldAppointments);
await _dbContext.SaveChangesAsync();

// Good: Bulk delete in single SQL statement
await _dbContext.Appointments
    .Where(a => a.AppointmentDate < DateTime.Today.AddYears(-2))
    .ExecuteDeleteAsync();

6. Optimistic Concurrency

Using Row Version:

public class Patient : FullAuditedAggregateRoot<Guid>
{
    [Timestamp] // or [ConcurrencyCheck]
    public byte[] RowVersion { get; set; }

    public string Name { get; set; }
    public string Email { get; set; }
}

// Handle concurrency exception
try
{
    patient.Email = "newemail@example.com";
    await _dbContext.SaveChangesAsync();
}
catch (DbUpdateConcurrencyException ex)
{
    var entry = ex.Entries.Single();
    var databaseValues = await entry.GetDatabaseValuesAsync();

    if (databaseValues == null)
    {
        // Entity was deleted
        throw new EntityNotFoundException();
    }

    // Reload with current database values
    await entry.ReloadAsync();

    // Or merge values
    var databasePatient = (Patient)databaseValues.ToObject();
    // Apply custom merge logic
}

7. PostgreSQL-Specific Features

Array Operations:

// Model with array
public class Patient
{
    public string[] Allergies { get; set; }
    public int[] ChronicConditionCodes { get; set; }
}

// Query arrays
var patientsWithPenicillinAllergy = await _dbContext.Patients
    .Where(p => p.Allergies.Contains("Penicillin"))
    .ToListAsync();

// Array overlap
var patientsWithAnyAllergy = await _dbContext.Patients
    .Where(p => p.Allergies.Any(a => new[] { "Penicillin", "Latex" }.Contains(a)))
    .ToListAsync();

// Configure in OnModelCreating
modelBuilder.Entity<Patient>()
    .Property(p => p.Allergies)
    .HasColumnType("text[]");

JSON Columns (JSONB):

// Model with JSON
public class MedicalRecord
{
    public Guid Id { get; set; }
    public JsonDocument Metadata { get; set; } // System.Text.Json
    // Or use custom type
    public Dictionary<string, object> CustomData { get; set; }
}

// Configure JSONB column
modelBuilder.Entity<MedicalRecord>()
    .Property(m => m.Metadata)
    .HasColumnType("jsonb");

// Query JSON properties
var records = await _dbContext.MedicalRecords
    .Where(m => EF.Functions.JsonContains(
        m.Metadata,
        @"{""diagnosis"": ""hypertension""}"))
    .ToListAsync();

Full-Text Search:

// Configure full-text search
modelBuilder.Entity<Patient>()
    .HasGeneratedTsVectorColumn(
        p => p.SearchVector,
        "english",
        p => new { p.Name, p.Email })
    .HasIndex(p => p.SearchVector)
    .HasMethod("GIN");

public class Patient
{
    public NpgsqlTsVector SearchVector { get; set; }
}

// Search
var patients = await _dbContext.Patients
    .Where(p => p.SearchVector.Matches(EF.Functions.ToTsQuery("english", "john & doe")))
    .ToListAsync();

Range Types:

public class DoctorSchedule
{
    public NpgsqlRange<TimeOnly> WorkingHours { get; set; }
}

// Query ranges
var schedulesAtTime = await _dbContext.DoctorSchedules
    .Where(s => s.WorkingHours.Contains(TimeOnly.FromDateTime(DateTime.Now)))
    .ToListAsync();

8. Query Optimization Techniques

Projection to DTOs:

// Bad: Load entire entity when only few fields needed
var patients = await _dbContext.Patients
    .Include(p => p.Appointments)
    .ToListAsync();

var result = patients.Select(p => new PatientListDto
{
    Id = p.Id,
    Name = p.Name
}).ToList();

// Good: Project directly to DTO
var patients = await _dbContext.Patients
    .Select(p => new PatientListDto
    {
        Id = p.Id,
        Name = p.Name,
        AppointmentCount = p.Appointments.Count
    })
    .ToListAsync();

Avoid Multiple Roundtrips:

// Bad: N+1 query problem
var appointments = await _dbContext.Appointments.ToListAsync();
foreach (var appointment in appointments)
{
    var patient = await _dbContext.Patients.FindAsync(appointment.PatientId);
    // Process...
}

// Good: Single query with Include
var appointments = await _dbContext.Appointments
    .Include(a => a.Patient)
    .ToListAsync();

Use FromSqlRaw for Complex Queries:

// When LINQ translation is inefficient
var statistics = await _dbContext.Appointments
    .FromSqlRaw(@"
        SELECT
            a.*,
            COUNT(*) OVER (PARTITION BY a.doctor_id) as doctor_appointment_count
        FROM appointments a
        WHERE a.appointment_date >= @startDate",
        new NpgsqlParameter("@startDate", startDate))
    .ToListAsync();

Query Filters for Soft Delete:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // Global query filter
    modelBuilder.Entity<Patient>()
        .HasQueryFilter(p => !p.IsDeleted);

    // Automatically applied to all queries
}

// Ignore filter when needed
var allPatients = await _dbContext.Patients
    .IgnoreQueryFilters()
    .ToListAsync();

9. Performance Monitoring

Log Generated SQL:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder
        .UseNpgsql(connectionString)
        .LogTo(Console.WriteLine, LogLevel.Information)
        .EnableSensitiveDataLogging() // Development only
        .EnableDetailedErrors();
}

Use ToQueryString for Debugging:

var query = _dbContext.Patients
    .Where(p => p.IsActive)
    .Include(p => p.Appointments);

var sql = query.ToQueryString();
Logger.LogInformation("Generated SQL: {Sql}", sql);

Best Practices

1. Use AsNoTracking for read-only queries
2. Project to DTOs when you don't need full entities
3. Split Queries for multiple includes to avoid cartesian explosion
4. Compiled Queries for frequently executed queries
5. Batch Operations (ExecuteUpdate/Delete) for bulk operations
6. Explicit Loading when you conditionally need related data
7. Avoid Lazy Loading in production (causes N+1 queries)
8. Use Query Filters for cross-cutting concerns (soft delete, multi-tenancy)
9. Monitor Generated SQL to identify inefficient queries
10. Use PostgreSQL Features (arrays, JSONB, FTS) when appropriate

Common Pitfalls

• N+1 Queries: Always use Include or explicit loading
• Cartesian Explosion: Use AsSplitQuery for multiple includes
• Tracking Overhead: Use AsNoTracking for read-only operations
• Loading Too Much Data: Project to DTOs instead of loading full entities
• Lazy Loading in Loops: Causes severe performance issues
• Not Using Compiled Queries: For hot paths
• Ignoring Query Filters: Can expose soft-deleted data

Performance Checklist

• Read-only queries use AsNoTracking()
• DTOs used instead of entities for lists
• Multiple includes use AsSplitQuery()
• No N+1 queries (verified with SQL logging)
• Compiled queries for hot paths
• Bulk operations use ExecuteUpdate/Delete
• Appropriate indexes on database
• Query filters configured for soft delete
• Change tracker cleared in batch operations
• PostgreSQL-specific features utilized

Resources

• EF Core Documentation: https://docs.microsoft.com/en-us/ef/core/
• Performance Best Practices: https://docs.microsoft.com/en-us/ef/core/performance/
• Npgsql EF Core Provider: https://www.npgsql.org/efcore/