EF6 中tracking log使用方法总结

先上一段最近项目中的代码，此代码可以放到自己项目中的dbContext中

public override Task<int> SaveChangesAsync()
        {
            List<AuditLog> AuditLogs = new List<AuditLog>();
            List<DataLensTrackingLog> trackinglogs = new List<DataLensTrackingLog>();
            var changeTracker = ChangeTracker.Entries().Where(p => p.State == EntityState.Added || p.State == EntityState.Deleted || p.State == EntityState.Modified);
            try
            {
                foreach (var entity in changeTracker)
                {
                    AuditLogs.Clear();
                    XmlDocument doc = new XmlDocument();
                    doc.AppendChild(doc.CreateElement(TrackingLog.Records));
                    if (entity.Entity != null)
                    {
                        var entityName = ObjectContext.GetObjectType(entity.Entity.GetType()).Name;
                        //string entityName = entity.Entity.GetType().Name;
                        EntityState state = entity.State;
                        switch (entity.State)
                        {
                            case EntityState.Modified:
                                //entityName = ObjectContext.GetObjectType(entity.Entity.GetType()).Name;
                                foreach (string prop in entity.OriginalValues.PropertyNames)
                                {
                                    object currentValue = entity.CurrentValues[prop];
                                    object originalValue = entity.GetDatabaseValues()[prop];//OriginalValues[prop];
                                    if (!Object.Equals(currentValue, originalValue)&&entity.Property(prop).IsModified==true
                                        &&prop.ToLower()!="lastupdateby")
                                    {
                                        AuditLogs.Add(new AuditLog
                                        {
                                            EntityName = entityName,
                                            RecordID = PrimaryKeyValue(entity),
                                            State = state,
                                            ColumnName = prop,
                                            OriginalValue = Convert.ToString(originalValue),
                                            NewValue = Convert.ToString(currentValue),
                                        });
                                    }
                                }
                                if (AuditLogs.Count > )
                                {
                                    TrackingLog.GetXmlForUpdate(doc, AuditLogs);
                                    trackinglogs.Add(new DataLensTrackingLog
                                    {
                                        EntityName = entityName,
                                        Email = this.Email,
                                        XmlDoc = CompressionHelper.Compresse("XmlDoc", new UTF8Encoding().GetBytes(doc.OuterXml)),
                                        CreateTime = DateTime.Now
                                    });
                                }
                                break;
                            case EntityState.Added:
                                //entityName = ObjectContext.GetObjectType(entity.Entity.GetType()).Name;
                                foreach (string prop in entity.CurrentValues.PropertyNames)
                                {
                                    AuditLogs.Add(new AuditLog
                                    {
                                        EntityName = entityName,
                                        RecordID = PrimaryKeyValue(entity),
                                        State = state,
                                        ColumnName = prop,
                                        OriginalValue = string.Empty,
                                        NewValue = entity.CurrentValues[prop],
                                    });

                                }
                                TrackingLog.GetXmlForUpdate(doc, AuditLogs);
                                trackinglogs.Add(new DataLensTrackingLog
                                {
                                    EntityName = entityName,
                                    Email = this.Email,
                                    XmlDoc = CompressionHelper.Compresse("XmlDoc", new UTF8Encoding().GetBytes(doc.OuterXml)),
                                    CreateTime = DateTime.Now
                                });
                                break;
                            case EntityState.Deleted:
                                //entityName = ObjectContext.GetObjectType(entity.Entity.GetType()).Name;
                                foreach (string prop in entity.OriginalValues.PropertyNames)
                                {
                                    AuditLogs.Add(new AuditLog
                                    {
                                        EntityName = entityName,
                                        RecordID = PrimaryKeyValue(entity),
                                        State = state,
                                        ColumnName = prop,
                                        OriginalValue = entity.OriginalValues[prop],
                                        NewValue = string.Empty,
                                    });

                                }
                                TrackingLog.GetXmlForUpdate(doc, AuditLogs);
                                trackinglogs.Add(new DataLensTrackingLog
                                {
                                    EntityName = entityName,
                                    Email = this.Email,
                                    XmlDoc = CompressionHelper.Compresse("XmlDoc", new UTF8Encoding().GetBytes(doc.OuterXml)),
                                    CreateTime = DateTime.Now
                                });
                                break;
                            default:
                                break;
                        }
                    }
                }
                DataTable dt=TypeConvert.ToDataTable(trackinglogs);
                SqlDataHelper.SqlBulkCopy(dt, "DataLensTrackingLog", DataBaseType.ConnLogDataStr);
                return base.SaveChangesAsync();
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

EF6中可以覆写SaveChangesAsync(异步)或者SaveChanges来实现记录变化的跟踪，这其中包括新增、修改、和删除，
dbContext中的属性ChangeTracker可以跟踪属性的变化,即查找实体修改记录：ChangeTracker.Entries().Where(p => p.State ==EntityState.Modified);
查找新增的实体记录行：ChangeTracker.Entries().Where(p => p.State == EntityState.Added);查找删除的实体记录行：
ChangeTracker.Entries().Where(p => p.State == EntityState.Deleted)

获取实体的名字是ObjectContext.GetObjectType(entity.Entity.GetType()).Name，之前获取实体是通过以下方式：
entity.Entity.GetType().Name，但是这种方式会有一个问题，假如说存在以下实体

public partial class DataLensDataPointUniverse
{
[Key]
public int DataPointUniverseId { get; set; }
public int DomicileId { get; set; }
public int ShareClassUniverseId { get; set; }
public int DataPointId { get; set; }
public int CollectionStatusId { get; set; }
public Nullable<System.DateTime> CollectionStartDate { get; set; }
public Nullable<System.DateTime> CollectionEndDate { get; set; }
public int CollectionFrequencyId { get; set; }
public int CollectionPriorityId { get; set; }
public string Restrictions { get; set; }
public int FundFormId { get; set; }
public string InterpretationRules { get; set; }
public string Comments { get; set; }
public string QualityMeasureCompleteness { get; set; }
public string QualityMeasureTimeliness { get; set; }
public string QualityMeasureAccuracy { get; set; }
public int FundCollectionRequirementId { get; set; }
public int LEANProjectId { get; set; }
public Nullable<System.Guid> CreateBy { get; set; }
public Nullable<System.Guid> LastUpdateBy { get; set; }
public Nullable<System.DateTime> CreateDate { get; set; }
public Nullable<System.DateTime> LastUpdateDate { get; set; }

public virtual DataLensDataPoint DataLensDataPoint { get; set; }
}

这时候获取的实体名字就可能是类似于这种格式343434343_DataLensDataPoint_3434,为什么会存在这种格式呢，因为该实体中的DataPointId是另个属性 public virtual DataLensDataPoint DataLensDataPoint { get; set; }中的外键，即（即实体DataLensDataPoint中DataPointId）

     获取属性当前值entity.CurrentValues[prop](即还未保存到数据库)，获取数据库当前值entity.GetDatabaseValues()[prop]
其中的entity.Property(prop).IsModified==true属性是来判断确实该值要存到数据库中，才要去记录日志，因为在Save
之前可能有些实体属性被标记为不做更改entity.Property(prop).IsModified==false;

获取实体主键的值可以用以下方法

private string PrimaryKeyValue(DbEntityEntry entry)
{
var objectStateEntry = ((IObjectContextAdapter)this).ObjectContext.ObjectStateManager.GetObjectStateEntry(entry.Entity);
if (null == objectStateEntry.EntityKey.EntityKeyValues)
{
return string.Empty;
}
return string.Join(",", objectStateEntry.EntityKey.EntityKeyValues.Select(item => item.Value.ToString()).ToArray());
}

当我们进行数据批量修改的时候我们可以用到EntityFramework.Extended,而不至于一条条的去更新数据库，增添了与数据库的I/O次数,具体的github地址地址为：

https://github.com/loresoft/EntityFramework.Extended,但是同时会有个问题，我们就没法做entitiframework的tracking log的使用，即使用SaveChanges的时候捕捉不到任何变化，如果想使用批量，又能捕捉到变化，可以使用entitiframework来执行sql语句来批量更新，并且也能捕获到数据改变的情况，因为使用了SaveChanges()，参考链接为：http://www.cnblogs.com/wujingtao/p/5412329.html

Note:EntityFramework.Extended也支持事务.