如何在使用EF代码的.SaveChanges（）期间记录所有实体更改？

Question

I'm using EF code first . I'm using a base Repository for all my repositories and an IUnitofWork that inject to the repositories, too:

public interface IUnitOfWork : IDisposable
{
    IDbSet<TEntity> Set<TEntity>() where TEntity : class;
    int SaveChanges();
}

public class BaseRepository<T> where T : class
{
    protected readonly DbContext _dbContext;
    protected readonly IDbSet<T> _dbSet;


    public BaseRepository(IUnitOfWork uow)
    {
        _dbContext = (DbContext)uow;
        _dbSet = uow.Set<T>();
    }
    //other methods
}   

eg my OrderRepository is like this:

class OrderRepository: BaseRepository<Order>
{
    IUnitOfWork _uow;
    IDbSet<Order> _order;

    public OrderRepository(IUnitOfWork uow)
        : base(uow)
    {
        _uow = uow;
        _order = _uow.Set<Order>();
    }
    //other methods
}

And I use it in this way:

public void Save(Order order)
{
        using (IUnitOfWork uow = new MyDBContext())
        {
            OrderRepository repository = new OrderRepository(uow); 
            try
            {
               repository.ApplyChanges<Order>(order);    
               uow.SaveChanges();
            }  

        } 
}     

Is there any way to log change histories of all entities(include their navigation properties) during .SaveChanges() ? I want to log original values (before save occurs) and changed values (after save occurs).

Answer 1

You can get the before and after values for all changed entities by going through DbContext.ChangeTracker . Unfortunately the API is a little verbose:

var changeInfo = context.ChangeTracker.Entries()
            .Where (t => t.State == EntityState.Modified)
            .Select (t => new {
                Original = t.OriginalValues.PropertyNames.ToDictionary (pn => pn, pn => t.OriginalValues[pn]),
                Current = t.CurrentValues.PropertyNames.ToDictionary (pn => pn, pn => t.CurrentValues[pn]),
            });

You can modify that to include things like the type of the entity if you need that for your logging. There is also a ToObject() method on the DbPropertyValues (the type of OriginalValues and CurrentValues) you could call if you already have a way to log whole objects, although the objects returned from that method will not have their navigation properties populated.

You can also modify that code to get all entities in the context by taking out the Where clause, if that makes more sense given your requirements.

Answer 2

you have scared people away with the extra requirement

Include their navigation properties

This is simply a non trivial exercise. And if this is important, you should manage/track changes across references with code.

this is a sample covering this topic Undo changes in entity framework entities

There is a sample doing close top what you want here undo changes It can easily be converted to load before and after images elsewhere.

Given the ObjectState entry after DetectChanges is called, you can implement a simple entity by entity option. and per UOW. But the navigation / references version makes this very complex as you worded the requirement.

EDIT : How to access the changeList

     public class  Repository<TPoco>{
     /....
     public DbEntityEntry<T> Entry(T entity) { return Context.Entry(entity); }

     public virtual IList<ChangePair> GetChanges(object poco) {

        var changes = new List<ObjectPair>();
        var thePoco = (TPoco) poco;

        foreach (var propName in Entry(thePoco).CurrentValues.PropertyNames) {
            var curr = Entry(thePoco).CurrentValues[propName];
            var orig = Entry(thePoco).OriginalValues[propName];
            if (curr != null && orig != null) {
                if (curr.Equals(orig)) {
                    continue;
                }
            }
            if (curr == null && orig == null) {
                continue;
            }
            var aChangePair = new ChangePair {Key = propName, Current = curr, Original = orig};
            changes.Add(aChangePair);
        }
        return changes;
    }
    ///...  partial repository shown
    } 
// FYI the simple return structure

public class ChangePair {
    public string Key { get; set; }
    public object Original { get; set; }
    public object Current { get; set; }
 }

Answer 3

I have overridded the default SaveChanges method to log changes for add/update/delete in entity. Though it does not cover navigation property changes.
Based on this article: Using entity framework for auditing

public int SaveChanges(string userId)
    {
        int objectsCount;

        List<DbEntityEntry> newEntities = new List<DbEntityEntry>();

        // Get all Added/Deleted/Modified entities (not Unmodified or Detached)
        foreach (var entry in this.ChangeTracker.Entries().Where
            (x => (x.State == System.Data.EntityState.Added) ||
                (x.State == System.Data.EntityState.Deleted) ||
                (x.State == System.Data.EntityState.Modified)))
        {
            if (entry.State == System.Data.EntityState.Added)
            {
                newEntities.Add(entry);
            }
            else
            {
                // For each changed record, get the audit record entries and add them
                foreach (AuditLog changeDescription in GetAuditRecordsForEntity(entry, userId))
                {
                    this.AuditLogs.Add(changeDescription);
                }
            }
        }

        // Default save changes call to actually save changes to the database
        objectsCount = base.SaveChanges();

        // We don't have recordId for insert statements that's why we need to call this method again.
        foreach (var entry in newEntities)
        {
            // For each changed record, get the audit record entries and add them
            foreach (AuditLog changeDescription in GetAuditRecordsForEntity(entry, userId, true))
            {
                this.AuditLogs.Add(changeDescription);
            }

            // TODO: Think about performance here. We are calling db twice for one insertion.
            objectsCount += base.SaveChanges();
        }

        return objectsCount;
    }

    #endregion

    #region Helper Methods

    /// <summary>
    /// Helper method to create record description for Audit table based on operation done on dbEntity
    /// - Insert, Delete, Update
    /// </summary>
    /// <param name="dbEntity"></param>
    /// <param name="userId"></param>
    /// <returns></returns>
    private List<AuditLog> GetAuditRecordsForEntity(DbEntityEntry dbEntity, string userId, bool insertSpecial = false)
    {
        List<AuditLog> changesCollection = new List<AuditLog>();

        DateTime changeTime = DateTime.Now;

        // Get Entity Type Name.
        string tableName1 = dbEntity.GetTableName();

        // http://stackoverflow.com/questions/2281972/how-to-get-a-list-of-properties-with-a-given-attribute
        // Get primary key value (If we have more than one key column, this will need to be adjusted)
        string primaryKeyName = dbEntity.GetAuditRecordKeyName();

        int primaryKeyId = 0;
        object primaryKeyValue;

        if (dbEntity.State == System.Data.EntityState.Added || insertSpecial)
        {
            primaryKeyValue = dbEntity.GetPropertyValue(primaryKeyName, true);

            if(primaryKeyValue != null)
            {
                Int32.TryParse(primaryKeyValue.ToString(), out primaryKeyId);
            }                

            // For Inserts, just add the whole record
            // If the dbEntity implements IDescribableEntity,
            // use the description from Describe(), otherwise use ToString()
            changesCollection.Add(new AuditLog()
                    {
                        UserId = userId,
                        EventDate = changeTime,
                        EventType = ModelConstants.UPDATE_TYPE_ADD,
                        TableName = tableName1,
                        RecordId = primaryKeyId,  // Again, adjust this if you have a multi-column key
                        ColumnName = "ALL",    // To show all column names have been changed
                        NewValue = (dbEntity.CurrentValues.ToObject() is IAuditableEntity) ?
                                        (dbEntity.CurrentValues.ToObject() as IAuditableEntity).Describe() :
                                        dbEntity.CurrentValues.ToObject().ToString()
                    }
                );
        }

        else if (dbEntity.State == System.Data.EntityState.Deleted)
        {
            primaryKeyValue = dbEntity.GetPropertyValue(primaryKeyName);

            if (primaryKeyValue != null)
            {
                Int32.TryParse(primaryKeyValue.ToString(), out primaryKeyId);
            }

            // With deletes use whole record and get description from Describe() or ToString()
            changesCollection.Add(new AuditLog()
                    {
                        UserId = userId,
                        EventDate = changeTime,
                        EventType = ModelConstants.UPDATE_TYPE_DELETE,
                        TableName = tableName1,
                        RecordId = primaryKeyId,
                        ColumnName = "ALL",
                        OriginalValue = (dbEntity.OriginalValues.ToObject() is IAuditableEntity) ?
                                    (dbEntity.OriginalValues.ToObject() as IAuditableEntity).Describe() :
                                    dbEntity.OriginalValues.ToObject().ToString()
                    });
        }

        else if (dbEntity.State == System.Data.EntityState.Modified)
        {
            primaryKeyValue = dbEntity.GetPropertyValue(primaryKeyName);

            if (primaryKeyValue != null)
            {
                Int32.TryParse(primaryKeyValue.ToString(), out primaryKeyId);
            }

            foreach (string propertyName in dbEntity.OriginalValues.PropertyNames)
            {
                // For updates, we only want to capture the columns that actually changed
                if (!object.Equals(dbEntity.OriginalValues.GetValue<object>(propertyName),
                        dbEntity.CurrentValues.GetValue<object>(propertyName)))
                {
                    changesCollection.Add(new AuditLog()
                    {
                        UserId = userId,
                        EventDate = changeTime,
                        EventType = ModelConstants.UPDATE_TYPE_MODIFY,
                        TableName = tableName1,
                        RecordId = primaryKeyId,
                        ColumnName = propertyName,
                        OriginalValue = dbEntity.OriginalValues.GetValue<object>(propertyName) == null ? null : dbEntity.OriginalValues.GetValue<object>(propertyName).ToString(),
                        NewValue = dbEntity.CurrentValues.GetValue<object>(propertyName) == null ? null : dbEntity.CurrentValues.GetValue<object>(propertyName).ToString()
                    }
                        );
                }
            }
        }


        // Otherwise, don't do anything, we don't care about Unchanged or Detached entities
        return changesCollection;
    }

Answer 4

DbContext has ChangeTracker property. You can override .SaveChanges() in your context and log changes. I don't think that entity framework can do it for you. Probably, you must detect changes directly in your model classes.