c# - Linq 2 SQL - 通用 where 子句

Question

有没有办法做到这一点

public T GetItemById(int id)
{
    Table<T> table = _db.GetTable<T>();
    table.Where(t => t.Id == id);
}

注意 i.Id 在上下文中不存在，因为 linq 不知道它正在使用什么对象，而 Id 是表的主键

Answer 1

(删除了绑定(bind)到属性的方法)

编辑:这是元模型方式(因此它适用于映射文件和属性对象):

static TEntity Get<TEntity>(this DataContext ctx, int key) where TEntity : class
{
    return Get<TEntity, int>(ctx, key);
}
static TEntity Get<TEntity, TKey>(this DataContext ctx, TKey key) where TEntity : class
{
    var table = ctx.GetTable<TEntity>();
    var pkProp = (from member in ctx.Mapping.GetMetaType(typeof(TEntity)).DataMembers
                  where member.IsPrimaryKey
                  select member.Member).Single();
    ParameterExpression param = Expression.Parameter(typeof(TEntity), "x");
    MemberExpression memberExp;
    switch (pkProp.MemberType)
    {
        case MemberTypes.Field: memberExp = Expression.Field(param, (FieldInfo)pkProp); break;
        case MemberTypes.Property: memberExp = Expression.Property(param, (PropertyInfo)pkProp); break;
        default: throw new NotSupportedException("Invalid primary key member: " + pkProp.Name);
    }
    Expression body = Expression.Equal(
        memberExp, Expression.Constant(key, typeof(TKey)));
    var predicate = Expression.Lambda<Func<TEntity, bool>>(body, param);
    return table.Single(predicate);
}