DbSet 在 EF7 中没有 Find 方法 [英] DbSet doesn't have a Find method in EF7

问题描述

我正在尝试创建一个通用存储库来访问我的数据库.在 EF6 中，我能够这样做以获得特定实体:

I am trying to create a generic repository to access my database. In EF6 I was able to do that in order to get a specific entity:

protected IDbSet<T> dbset;

public T Get(object id)
{
    return this.dbset.Find(id);
}

EF7 中的 DbSet 缺少 Find 方法.有没有办法实现上面这段代码?

DbSet in EF7 is missing a Find method. Is there a way to implement the above piece of code?

推荐答案

这里是作为扩展方法的 .Find() 的一个非常粗糙、不完整且未经测试的实现.如果不出意外，它应该能让你指明正确的方向.

Here's a very crude, incomplete, and untested implementation of .Find() as an extension method. If nothing else, it should get you pointed in the right direction.

实际实现由 #797 跟踪.

static TEntity Find<TEntity>(this DbSet<TEntity> set, params object[] keyValues)
    where TEntity : class
{
    var context = ((IAccessor<IServiceProvider>)set).Service.GetService<DbContext>();

    var entityType = context.Model.GetEntityType(typeof(TEntity));
    var key = entityType.GetPrimaryKey();

    var entries = context.ChangeTracker.Entries<TEntity>();

    var i = 0;
    foreach (var property in key.Properties)
    {
        var keyValue = keyValues[i];
        entries = entries.Where(e => e.Property(property.Name).CurrentValue == keyValue);
        i++;
    }

    var entry = entries.FirstOrDefault();
    if (entry != null)
    {
        // Return the local object if it exists.
        return entry.Entity;
    }

    // TODO: Build the real LINQ Expression
    // set.Where(x => x.Id == keyValues[0]);
    var parameter = Expression.Parameter(typeof(TEntity), "x");
    var query = set.Where((Expression<Func<TEntity, bool>>)
        Expression.Lambda(
            Expression.Equal(
                Expression.Property(parameter, "Id"),
                Expression.Constant(keyValues[0])),
            parameter));

    // Look in the database
    return query.FirstOrDefault();
}

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