EF7 - 如何在更改之前从 DbSet 获取值

本文关键字：DbSet 获取 EF7 | 更新日期: 2023-09-27 18:32:13

我尝试获取存储在 DbSet 中的实体的值，该实体在被代码更改之前和保存之前。但是，当我尝试使用 LINQ Single语句获取它时，我得到了更改的值。我正在使用 EF7。

代码如下：

DbSet<Entity> dbSet = Context.dbSet;
Entity ent = dbSet.Single(x => x.Id == id);
ent.FirstName = "New name";
Entity entityBeforeChange = dbSet.Single(x => x.Id == id);  //here I want to get entity with old values, if that's important I just need to read it without modifying this instance
Context.SaveChanges();

希望我足够清楚，可以得到一些帮助

EF7 - 如何在更改之前从 DbSet 获取值

您可以从ChangeTracker中获取任何实体的原始值。

var original = Context.ChangeTracker.Entries<Entity>().Single(x => x.Id == id);
var firstName = original.Property<string>("FirstName").OriginalValue;

这是我从审计库中使用的代码。

EF7 

using (var ctx = new TestContext())
{
    Entity ent = entity.Single(x => x.Id == id);
    entity.FirstName = "New name";
    context.ChangeTracker.DetectChanges();
    // Find your entry or get all changed entries
    var changes = context.ChangeTracker.Entries().Where(x => x.State == EntityState.Modified);
    foreach (var objectStateEntry in changes)
    {
        AuditEntityModified(audit, objectStateEntry, auditState);
    }
}
public static void AuditEntityModified(Audit audit, AuditEntry entry, EntityEntry objectStateEntry)
{
    foreach (var propertyEntry in objectStateEntry.Metadata.GetProperties())
    {
        var property = objectStateEntry.Property(propertyEntry.Name);
        if (entry.Parent.CurrentOrDefaultConfiguration.IsAudited(entry.ObjectStateEntry, propertyEntry.Name))
        {
            entry.Properties.Add(new AuditEntryProperty(entry, propertyEntry.Name, property.OriginalValue, property.CurrentValue));
        }
    }
}

EF6

using (var ctx = new TestContext())
{
    Entity ent = entity.Single(x => x.Id == id);
    entity.FirstName = "New name";
    var entry = ((IObjectContextAdapter)ctx).ObjectContext.ObjectStateManager.GetObjectStateEntry(entity);
    var currentValues = entry.CurrentValues;
    var originalValues = entry.OriginalValues;
    AuditEntityModified(originalValues, currentValues);
}
public static void AuditEntityModified(DbDataRecord orginalRecord, DbUpdatableDataRecord currentRecord, string prefix = "")
{
    for (var i = 0; i < orginalRecord.FieldCount; i++)
    {
        var name = orginalRecord.GetName(i);
        var originalValue = orginalRecord.GetValue(i);
        var currentValue = currentRecord.GetValue(i);
        var valueRecord = originalValue as DbDataRecord;
        if (valueRecord != null)
        {
            // Complex Type
            AuditEntityModified(valueRecord, currentValue as DbUpdatableDataRecord, string.Concat(prefix, name, "."));
        }
        else
        {
            if (!Equals(currentValue, originalValue))
            {
                // Add modified values
            }
        }
    }
}

编辑：完整的源代码可以在我的GitHub存储库中找到：https://github.com/zzzprojects/EntityFramework-Plus

图书馆网站： http://entityframework-plus.net/

您可以从

上下文中Detach实体。请记住，在更新另一个附加实体之前，必须将其从上下文中提取。

DbSet<Entity> dbSet = Context.dbSet;
Entity ent = dbSet.Single(x => x.Id == id);
Entity entityBeforeChange = dbSet.Single(x => x.Id == id); 
Context.Entry(entityBeforeChange).State = EntityState.Detached; // severs the connection to the Context
ent.FirstName = "New name";
Context.SaveChanges();

您可以使用新的 DbContext，因为加载的实体缓存在已有的实体中。

Entity oldUnchanged;
using (var ctx = new YourDbContext()) 
{
    oldUnchanged = ctx.Set<Entity>().Single(x => x.Id == id);
}
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