EntityFramework.CommonTools

Extension for EntityFramework and EntityFramework Core that provides: Expandable Extension Methods, Complex Types as JSON, Auditing, Concurrency Checks, Specifications and serializable Transacton Logs.

Documentation

• Expandable IQueryable Extensions
• JSON Complex Types
• Specification Pattern
• Auditable Entities
• Concurrency Checks
• Transaction Logs
• DbContext Extensions (EF 6 only)
• Usage with EntityFramework Core
• Usage with EntityFramework 6
• Changelog

NuGet

PM> Install-Package EntityFramework.CommonTools

PM> Install-Package EntityFrameworkCore.CommonTools

Attaching ExpressionVisitor to IQueryable

With .AsVisitable() extension we can attach any ExpressionVisitor to IQueryable<T>.

public static IQueryable<T> AsVisitable<T>(
    this IQueryable<T> queryable, params ExpressionVisitor[] visitors);

Expandable extension methods for IQueryable

We can use extension methods for IQueryable<T> to incapsulate custom buisiness logic.
But if we call these methods from Expression<TDelegate>, we get runtime error.

public static IQueryable<Post> FilterByAuthor(this IQueryable<Post> posts, int authorId)
{
    return posts.Where(p => p.AuthorId = authorId);
}

public static IQueryable<Comment> FilterTodayComments(this IQueryable<Comment> comments)
{
    DateTime today = DateTime.Now.Date;

    return comments.Where(c => c.CreationTime > today)
}

Comment[] comments = context.Posts
    .FilterByAuthor(authorId)   // it's OK
    .SelectMany(p => p.Comments
        .AsQueryable()
        .FilterTodayComments()) // will throw Error
    .ToArray();

With .AsExpandable() extension we can use extension methods everywhere.

Comment[] comments = context.Posts
    .AsExpandable()
    .FilterByAuthor(authorId)   // it's OK
    .SelectMany(p => p.Comments
        .FilterTodayComments()) // it's OK too
    .ToArray();

Expandable extension methods should return IQueryable and should have [Expandable] attribute.

[Expandable]
public static IQueryable<Post> FilterByAuthor(this IEnumerable<Post> posts, int authorId)
{
    return posts.AsQueryable().Where(p => p.AuthorId = authorId);
}

[Expandable]
public static IQueryable<Comment> FilterTodayComments(this IEnumerable<Comment> comments)
{
    DateTime today = DateTime.Now.Date;

    return comments.AsQueryable().Where(c => c.CreationTime > today)
}

Benchmarks

          Method |        Median |     StdDev | Scaled | Scaled-SD |
---------------- |-------------- |----------- |------- |---------- |
        RawQuery |   555.6202 μs | 15.1837 μs |   1.00 |      0.00 |
 ExpandableQuery |   644.6258 μs |  3.7793 μs |   1.15 |      0.03 | <<<
  NotCachedQuery | 2,277.7138 μs | 10.9754 μs |   4.06 |      0.10 |

JSON Complex Types

There is an utility struct named JsonField, that helps to persist any Complex Type as JSON string in single table column.

struct JsonField<TObject>
    where TObject : class
{
    public string Json { get; set; }
    public TObject Object { get; set; }
}

Usage:

class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Login { get; set; }

    private JsonField<Address> _address;
    // used by EntityFramework
    public string AddressJson
    {
        get { return _address.Json; }
        set { _address.Json = value; }
    }
    // used by application code
    public Address Address
    {
        get { return _address.Object; }
        set { _address.Object = value; }
    }

    // collection initialization by default
    private JsonField<ICollection<string>> _phones = new HashSet<string>();
    public string PhonesJson
    {
        get { return _phones.Json; }
        set { _phones.Json = value; }
    }
    public ICollection<string> Phones
    {
        get { return _phones.Object; }
        set { _phones.Object = value; }
    }
}

[NotMapped]
class Address
{
    public string City { get; set; }
    public string Street { get; set; }
    public string Building { get; set; }
}

If we update these Complex Type properties, the following SQL is generated during SaveChanges:

UPDATE Users
SET AddressJson = '{"City":"Moscow","Street":"Arbat","Building":"10"}',
    PhonesJson = '["+7 (123) 456-7890","+7 (098) 765-4321"]'
WHERE Id = 1;

The AddressJson property is serialized from Address only when it accessed by EntityFramework.
And the Address property is materialized from AddressJson only when EntityFramework writes to AddressJson.

If we want to initialize some JSON collection in entity consctuctor, for example:

class MyEntity
{
    public ICollection<MyObject> MyObjects { get; set; } = new HashSet<MyObject>();
}

We can use the following implicit conversion:

class MyEntity
{
    private JsonField<ICollection<MyObject>> _myObjects = new HashSet<MyObject>();
}

It uses the following implicit operator:

struct JsonField<TObject>
{
    public static implicit operator JsonField<TObject>(TObject defaultValue);
}

The only caveat is that TObject object should not contain reference loops.
Because JsonField uses Jil (the fastest .NET JSON serializer) behind the scenes.

Specification Pattern

Generic implementation of Specification Pattern.

public interface ISpecification<T>
{
    bool IsSatisfiedBy(T entity);

    Expression<Func<T, bool>> ToExpression();
}

public class Specification<T> : ISpecification<T>
{
    public Specification(Expression<Func<T, bool>> predicate);
}

We can define named specifications:

class UserIsActiveSpec : Specification<User>
{
    public UserIsActiveSpec()
        : base(u => !u.IsDeleted) { }
}

class UserByLoginSpec : Specification<User>
{
    public UserByLoginSpec(string login)
        : base(u => u.Login == login) { }
}

Then we can combine specifications with conditional logic operators &&, || and !:

class CombinedSpec
{
    public CombinedSpec(string login)
        : base(new UserIsActiveSpec() && new UserByLoginSpec(login)) { }
}

Also we can test it:

var user = new User { Login = "admin", IsDeleted = false };
var spec = new CombinedSpec("admin");

Assert.IsTrue(spec.IsSatisfiedBy(user));

And use with IEnumerable<T>:

var users = Enumerable.Empty<User>();
var spec = new UserByLoginSpec("admin");

var admin = users.FirstOrDefault(spec.IsSatisfiedBy);

// or even
var admin = users.FirstOrDefault(spec);

Or even with IQueryable<T>:

var spec = new UserByLoginSpec("admin");

var admin = context.Users.FirstOrDefault(spec.ToExpression());

// or even
var admin = context.Users.FirstOrDefault(spec);

// and also inside Expression
var adminFiends = context.Users
    .AsVisitable(new SpecificationExpander())
    .Where(u => u.Firends.Any(spec.ToExpression()))
    .ToList();

// or even
var adminFiends = context.Users
    .AsVisitable(new SpecificationExpander())
    .Where(u => u.Firends.Any(spec))
    .ToList();

Auditable Entities

Automatically update info about who and when create / modify / delete the entity during context.SaveCahnges()

class User
{
    public int Id { get;set; }
    public string Login { get; set; }
}

class Post : IFullAuditable<int>
{
    public int Id { get; set; }
    public string Content { get; set; }
    
    // IFullAuditable<int> members
    public bool IsDeleted { get; set; }
    public int CreatorUserId { get; set; }
    public DateTime CreatedUtc { get; set; }
    public int? UpdaterUserId { get; set; }
    public DateTime? UpdatedUtc { get; set; }
    public int? DeleterUserId { get; set; }
    public DateTime? DeletedUtc { get; set; }
}

class MyContext : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Post> Posts { get; set; }

    public void SaveChanges(int editorUserId)
    {
        this.UpdateAuditableEntities(editorUserId);
        base.SaveChanges();
    }
}

Also you can track only the creation, deletion and so on by implementing the following interfaces:

ISoftDeletable

Used to standardize soft deleting entities. Soft-delete entities are not actually deleted, marked as IsDeleted == true in the database, but can not be retrieved to the application.

interface ISoftDeletable
{
    bool IsDeleted { get; set; }
}

ICreationTrackable

An entity can implement this interface if CreatedUtc of this entity must be stored. CreatedUtc is automatically set when saving Entity to database.

interface ICreationTrackable
{
    DateTime CreatedUtc { get; set; }
}

ICreationAuditable<TUserId>

This interface is implemented by entities that is wanted to store creation information (who and when created). Creation time and creator user are automatically set when saving Entity to database.

interface ICreationAuditable<TUserId> : ICreationTrackable
    where TUserId : struct
{
    TUserId CreatorUserId { get; set; }
}
// or
interface ICreationAuditable : ICreationTrackable
{
    string CreatorUserId { get; set; }
}

IModificationTrackable

An entity can implement this interface if UpdatedUtc of this entity must be stored. UpdatedUtc automatically set when updating the Entity.

interface IModificationTrackable
{
    DateTime? UpdatedUtc { get; set; }
}

IModificationAuditable<TUserId>

This interface is implemented by entities that is wanted to store modification information (who and when modified lastly). Properties are automatically set when updating the Entity.

interface IModificationAuditable<TUserId> : IModificationTrackable
    where TUserId : struct
{
    TUserId? UpdaterUserId { get; set; }
}
// or
interface IModificationAuditable : IModificationTrackable
{
    string UpdaterUserId { get; set; }
}

IDeletionTrackable

An entity can implement this interface if DeletedUtc of this entity must be stored. DeletedUtc is automatically set when deleting Entity.

interface IDeletionTrackable : ISoftDeletable
{
    DateTime? DeletedUtc { get; set; }
}

IDeletionAuditable<TUserId>

This interface is implemented by entities which wanted to store deletion information (who and when deleted).

public interface IDeletionAuditable<TUserId> : IDeletionTrackable
    where TUserId : struct
{
    TUserId? DeleterUserId { get; set; }
}
// or
public interface IDeletionAuditable : IDeletionTrackable
{
    string DeleterUserId { get; set; }
}

IFullTrackable

This interface is implemented by entities which modification times must be tracked. Related properties automatically set when saving/updating/deleting Entity objects.

interface IFullTrackable : ICreationTrackable, IModificationTrackable, IDeletionTrackable { }

IFullAuditable<TUserId>

This interface is implemented by entities which must be audited. Related properties automatically set when saving/updating/deleting Entity objects.

interface IFullAuditable<TUserId> : IFullTrackable,
    ICreationAuditable<TUserId>, IModificationAuditable<TUserId>, IDeletionAuditable<TUserId>
    where TUserId : struct { }
// or
interface IFullAuditable : IFullTrackable, ICreationAuditable, IModificationAuditable, IDeletionAuditable { }

You can choose between saving the user Id or the user Login.
So there are two overloadings for DbContext.UpdateAudiatbleEntities():

static void UpdateAuditableEntities<TUserId>(this DbContext context, TUserId editorUserId);
static void UpdateAuditableEntities(this DbContext context, string editorUserId);

and also the separate extension to update only Trackable entities:

static void UpdateTrackableEntities(this DbContext context);

Concurrency Checks

By default EF and EFCore uses EntityEntry.OriginalValues["RowVersion"] for concurrency checks (see docs).

With this behaviour the concurrency conflict may occur only between the SELECT statement that loads entities to the DbContext and the UPDATE statement from DbContext.SaveChanges().

But sometimes we want check concurrency conflicts between two or more edit operations that comes from client-side. For example:

• user_1 loads the editor form
• user_2 loads the same editor form
• user_1 saves his changes
• user_2 saves his changes and gets concurrency conflict.

To provide this behaviour, an entity should implement the following interface:

interface IConcurrencyCheckable<TRowVersion>
{
    TRowVersion RowVersion { get; set; }
}

And the DbContext should overload SaveChanges() method with UpdateConcurrentEntities() extension:

class MyDbContext : DbContext
{
    public override int SaveChanges()
    {
        this.UpdateConcurrentEntities();
        return base.SaveChanges();
    }
}

There are also three different behaviours for IConcurrencyCheckable<T>:

IConcurrencyCheckable<byte[]>

RowVersion property should be decorated by [Timestamp] attribute.
RowVersion column should have ROWVERSION type in SQL Server.
The default behaviour. Supported only by Microsoft SQL Server.

class MyEntity : IConcurrencyCheckable<Guid>
{
    [Timestamp]
    public byte[] RowVersion { get; set; }
}

IConcurrencyCheckable<Guid>

RowVersion property should be decorated by [ConcurrencyCheck] attribute.
It's value is populated by Guid.NewGuid() during each DbContext.SaveChanges() call at client-side.
No specific database support is needed.

class MyEntity : IConcurrencyCheckable<Guid>
{
    [ConcurrencyCheck]
    public Guid RowVersion { get; set; }
}

IConcurrencyCheckable<long>

RowVersion property should be decorated by [ConcurrencyCheck] and [DatabaseGenerated(DatabaseGeneratedOption.Computed)] attributes.

class MyEntity : IConcurrencyCheckable<long>
{
    [ConcurrencyCheck]
    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public long RowVersion { get; set; }
}

RowVersion column should be updated by trigger in DB. Example for SQLite:

CREATE TABLE MyEntities ( RowVersion INTEGER DEFAULT 0 );

CREATE TRIGGER TRG_MyEntities_UPD
AFTER UPDATE ON MyEntities
    WHEN old.RowVersion = new.RowVersion
BEGIN
    UPDATE MyEntities
    SET RowVersion = RowVersion + 1;
END;

But sometimes we want to ignore DbUpdateConcurrencyException. And there are two extension methods for this.

static void SaveChangesIgnoreConcurrency(this DbContext dbContext, int retryCount = 3)
Save changes regardless of DbUpdateConcurrencyException.

static async Task SaveChangesIgnoreConcurrencyAsync(this DbContext dbContext, int retryCount = 3)
Save changes regardless of DbUpdateConcurrencyException.

Transaction Logs

Write all inserted / updated / deleted entities (serialized to JSON) to the separete table named TransactionLog.

To capture transaction logs an entity must inherit from empty ITransactionLoggable { } interface.

And the DbContext should overload SaveChanges() method with SaveChangesWithTransactionLog() wrapper,
and register the TransactionLog entity in ModelBuilder.

class Post : ITransactionLoggable
{
    public string Content { get; set; }
}

// for EntityFramework 6
class MyDbContext : DbContext
{
    public DbSet<Post> Posts { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.UseTransactionLog();
    }

    public override int SaveChanges()
    {
        return this.SaveChangesWithTransactionLog(base.SaveChanges);
    }

    // override the most general SaveChangesAsync
    public override Task<int> SaveChangesAsync(CancellationToken cancellationToken)
    {
        return this.SaveChangesWithTransactionLogAsync(base.SaveChangesAsync, cancellationToken);
    }
}

// for EntityFramework Core
class MyCoreDbContext : DbContext
{
    public DbSet<Post> Posts { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.UseTransactionLog();
    }

    // override the most general SaveChanges
    public override int SaveChanges(bool acceptAllChangesOnSuccess)
    {
        return this.SaveChangesWithTransactionLog(base.SaveChanges, acceptAllChangesOnSuccess);
    }

    // override the most general SaveChangesAsync
    public override Task<int> SaveChangesAsync(
        bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default(CancellationToken))
    {
        return this.SaveChangesWithTransactionLogAsync(
            base.SaveChangesAsync, acceptAllChangesOnSuccess, cancellationToken);
    }
}

After that the transaction logs can be accessed via TransactionLog entity:

class TransactionLog
{
    // Auto incremented primary key.
    public long Id { get; set; }
    
    // An ID of all changes that captured during single DbContext.SaveChanges() call.
    public Guid TransactionId { get; set; }

    // UTC timestamp of DbContext.SaveChanges() call.
    public DateTime CreatedUtc { get; set; }

    // "INS", "UPD" or "DEL". Not null.
    public string Operation { get; set; }

    // Schema for captured entity. Can be null for SQLite.
    public string Schema { get; set; }

    // Table for captured entity. Not null.
    public string TableName { get; set; }

    // Assembly qualified type name of captured entity. Not null.
    public string EntityType { get; set; }

    // The captured entity serialized to JSON by Jil serializer. Not null.
    public string EntityJson { get; set; }

    // Lazily deserialized entity object.
    // Type for deserialization is taken from EntityType property.
    // All navigation properties and collections will be empty.
    public object Entity { get; }

    // Get strongly typed entity from transaction log.
    // Can be null if TEntity and type from EntityType property are incompatible.
    // All navigation properties and collections will be empty.
    public TEntity GetEntity<TEntity>();
}

For querying and indexing TransactionLogs table see #2.

DbContext Extensions (EF 6 only)

static IDisposable WithoutChangeTracking(this DbContext dbContext)
Disposable token for using(...) statement where DbContext.Configuration.AutoDetectChanges is disabled.

// here AutoDetectChanges is enabled
using (dbContext.WithoutChangeTracking())
{
    // inside this block AutoDetectChanges is disabled
}
// here AutoDetectChanges is enabled again

static IDisposable WithChangeTrackingOnce(this DbContext dbContext)
Run DbChangeTracker.DetectChanges() once and return disposable token for using(...) statement where DbContext.Configuration.AutoDetectChanges is disabled.

// here AutoDetectChanges is enabled
using (dbContext.WithChangeTrackingOnce())
{
    // inside this block AutoDetectChanges is disabled
}
// here AutoDetectChanges is enabled again

static TableAndSchema GetTableAndSchemaName(this DbContext context, Type entityType)
Get corresponding table name and schema by entityType.

static TableAndSchema[] GetTableAndSchemaNames(this DbContext context, Type entityType)
Get corresponding table name and schema by entityType. Use it if entity is splitted between multiple tables.

struct TableAndSchema
{
    public string TableName;
    public string Schema;
}

All together example for EntityFramework Core

class MyDbContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.UseTransactionLog();
    }

    // override the most general SaveChanges
    public override int SaveChanges(bool acceptAllChangesOnSuccess)
    {
        this.UpdateTrackableEntities();
        this.UpdateConcurrentEntities();

        return this.SaveChangesWithTransactionLog(base.SaveChanges, acceptAllChangesOnSuccess);
    }

    // override the most general SaveChangesAsync
    public override Task<int> SaveChangesAsync(
        bool acceptAllChangesOnSuccess, CancellationToken cancellationToken = default(CancellationToken))
    {
        this.UpdateTrackableEntities();
        this.UpdateConcurrentEntities();

        return this.SaveChangesWithTransactionLogAsync(
            base.SaveChangesAsync, acceptAllChangesOnSuccess, cancellationToken);
    }

    public int SaveChanges(int editorUserId)
    {
        this.UpdateAuditableEntities(editorUserId);
        
        return SaveChanges();
    }

    public Task<int> SaveChangesAsync(int editorUserId)
    {
        this.UpdateAuditableEntities(editorUserId);

        return SaveChangesAsync();
    }
}

All together example for EntityFramework 6

class MyDbContext : DbContext
{
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.UseTransactionLog();
    }

    // override the most general SaveChanges
    public override int SaveChanges()
    {
        using (this.WithChangeTrackingOnce())
        {
            this.UpdateTrackableEntities();
            this.UpdateConcurrentEntities();

            return this.SaveChangesWithTransactionLog(base.SaveChanges);
        }
    }

    // override the most general SaveChangesAsync
    public override Task<int> SaveChangesAsync(CancellationToken cancellationToken)
    {
        using (this.WithChangeTrackingOnce())
        {
            this.UpdateTrackableEntities();
            this.UpdateConcurrentEntities();

            return this.SaveChangesWithTransactionLogAsync(base.SaveChangesAsync, cancellationToken);
        }
    }

    public int SaveChanges(int editorUserId)
    {
        this.UpdateAuditableEntities(editorUserId);
        
        return SaveChanges();
    }

    public Task<int> SaveChangesAsync(int editorUserId)
    {
        this.UpdateAuditableEntities(editorUserId);

        return SaveChangesAsync();
    }
}

---

Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog and this project adheres to Semantic Versioning.

2.0.2 - 2018-05-10

Fixed

• context.Update(entity) does not reset ICreationTrackable.CreatedUtc and ICreationAuditable.CreatorUserId to empty values #4

2.0.1 - 2018-03-27

Fixed

• .AsExpandable() works with bound lambda arguments

2.0.0 - 2018-03-23

Added

• EFCore 2.0 support
• EntityFramework 6.2 support

Changed

• ICreationAuditable.CreatorUser renamed to CreatorUserId
• IModificationAuditable.UpdaterUser renamed to UpdaterUserId
• IDeletionAuditable.DeleterUser renamed to DeleterUserId

See #1.

For compatibility issues you still can use these interfaces:

public interface ICreationAuditableV1
{
    string CreatorUser { get; set; }
}

public interface IModificationAuditableV1
{
    string UpdaterUser { get; set; }
}

public interface IDeletionAuditableV1
{
    string DeleterUser { get; set; }
}

public interface IFullAuditableV1 : IFullTrackable,
    ICreationAuditableV1, IModificationAuditableV1, IDeletionAuditableV1
{
}

1.0.0 - 2017-08-16

Added

Initial project version.