Question

我有这段代码。

var menucategories = db.Menus.Where(m => m.Language.lang_code == lang && m.published == 1).OrderBy(m => m.ordering).ToList();

使用此代码，我想获取所有可用的菜单类型并导入DBContext内存。

db.MenuTypes.ToList();

foreach (var item in menucategories)
{
    if (item.published == 1)
    {
        //Search into the DBContext memory for the MenuTypes
        var view = db.MenuTypes.Find(item.menu_type_fk_id);
         ....

在这个foreach循环中，我使用db.MenuTypes.Find(item.menu_type_fk_id)语句。我的问题是，这个Find方法是否会往返数据库或搜索到DBContext内存？

Answer 1

您可以阅读documentation：

DbSet<TEntity>.Find:查找具有给定主键值的实体。 如果上下文中存在具有给定主键值的实体，则会立即返回该实体而不向商店发出请求。否则，将向具有给定主要实体的实体发出请求键值和此实体（如果找到）将附加到上下文并返回。如果在上下文或商店中找不到实体，则返回null。

根据这一点，如果在使用Find方法之前将记录加载到内存中，Find方法将从缓存中返回记录，否则它将向db发送查询。您也可以使用Sql Profiler轻松测试。在你调用Find方法的行上设一个断点，然后看看会发生什么。

Answer 2

查找首先查看stateManager ... （上下文），如果找不到，则在商店中查找...
用resharper点击2次。与代码一致的文档; - ）

public TEntity Find(params object[] keyValues)
{
  this.InternalContext.ObjectContext.AsyncMonitor.EnsureNotEntered();
  this.InternalContext.DetectChanges(false);
  WrappedEntityKey key = new WrappedEntityKey(this.EntitySet, this.EntitySetName, keyValues, "keyValues");
  object obj = this.FindInStateManager(key) ?? this.FindInStore(key, "keyValues");
  if (obj != null && !(obj is TEntity))
    throw Error.DbSet_WrongEntityTypeFound((object) obj.GetType().Name, (object) typeof (TEntity).Name);
  else
    return (TEntity) obj;
}


/// <summary>
/// Finds an entity with the given primary key values.
///             If an entity with the given primary key values exists in the context, then it is
///             returned immediately without making a request to the store.  Otherwise, a request
///             is made to the store for an entity with the given primary key values and this entity,
///             if found, is attached to the context and returned.  If no entity is found in the
///             context or the store, then null is returned.
/// 
/// </summary>
/// 
/// <remarks>
/// The ordering of composite key values is as defined in the EDM, which is in turn as defined in
///             the designer, by the Code First fluent API, or by the DataMember attribute.
/// 
/// </remarks>
/// <param name="keyValues">The values of the primary key for the entity to be found. </param>
/// <returns>
/// The entity found, or null.
/// </returns>
/// <exception cref="T:System.InvalidOperationException">Thrown if multiple entities exist in the context with the primary key values given.</exception><exception cref="T:System.InvalidOperationException">Thrown if the type of entity is not part of the data model for this context.</exception><exception cref="T:System.InvalidOperationException">Thrown if the types of the key values do not match the types of the key values for the entity type to be found.</exception><exception cref="T:System.InvalidOperationException">Thrown if the context has been disposed.</exception>
public virtual TEntity Find(params object[] keyValues)
{
  return this.GetInternalSetWithCheck("Find").Find(keyValues);
}

ToList和Find实现

2 个答案: