我可以在linqto实体中动态构建where子句吗?

我正在尝试为linqto实体动态构建一个LINQ查询,这样就可以避免重复同一个函数两次。

我想做的是:

private IUser GetOrUpdateUser(Predicate<IUser> filter, Func<IIdentityProvider, UserRecord> fetch)
{
    var user = (from u in this.adapter.Users
                where filter(u)
                select u).SingleOrDefault();

    if (user == null)
    {
        // User not found.  Add him.
        user = this.adapter.AddUser(fetch(this.idenityProvider));
    }
    else if (user.IsExpired)
    {
        // User found, but expired.  Update him.
        this.adapter.UpdateUser(user, fetch(this.idenityProvider));
    }

    return user;
}

protected IUser GetUserByNetworkId(string username)
{
    return GetOrUpdateUser(
        u => u.NetworkId == username,
        i => i.GetUserByNetworkId(username));
}

protected IUser GetUserByEmail(string email)
{
    return GetOrUpdateUser(
        u => u.Email == email,
        i => i.GetUserByEmail(email));
}

这个 filter

protected IUser GetUserByNetworkId(string username)
{
    return GetOrUpdateUser(
        from u in this.adapter.Users
        where u.NetworkId == username
        select u,
        i => i.GetUserByNetworkId(username));
}

protected IUser GetUserByEmail(string email)
{
    return GetOrUpdateUser(
        from u in this.adapter.Users
        where u.Email == email
        select u,
        i => i.GetUserByEmail(email));
}