Csharp 为什么方法的值在SELECT方法中不会更改

我有一个方法可以从postgres中的序列返回值:

public long GetSId(DatabaseFacade d, string sequenceName)
{
    var result = new NpgsqlParameter(":result", NpgsqlDbType.Integer)
    {
        Direction = System.Data.ParameterDirection.InputOutput,
        Value = 0
    };
    d.ExecuteSqlRaw($"SELECT nextval('{sequenceName}')", result);
    return (long)result.Value;
}

我有一种形成数据的方法:

private List<CrossingsResult> FormCrossingResult()
{
    var d = _dbContext.Database;
    var crosswalks = _dbContext.Crosswalks
        .Select(x => new CrossingsResult
        {
            SId = GetSId(d, _sequenceName),
            ...
        }).ToList();
    return crosswalks;

问题是，当我在Select中调用方法时，SID不会改变(例如，它会为所有记录设置相同的SID值).但如果我在人行横道外调用该方法，它会起作用 就像这样:

private List<CrossingsResult> FormCrossingResult()
{
    var d = _dbContext.Database;
    Console.WriteLine($"First call: {GetSId(d, _sequenceName)}");
    Console.WriteLine($"Second call: {GetSId(d, _sequenceName)}");
    Console.WriteLine($"Third call: {GetSId(d, _sequenceName)}");
    var crosswalks = _dbContext.Crosswalks
        .Select(x => new CrossingsResult
        {
            SId = GetSId(d, _sequenceName),
            ...
        }).ToList();
    foreach (var crosswalk in crosswalks)
    {
        Console.WriteLine(crosswalk.SId);
    }
    return crosswalks;

Result be like this:

我试着用for循环来做它，它起作用了:

private List<CrossingsResult> FormCrossingResult()
{
    var d = _dbContext.Database;
    var crosswalks = _dbContext.Crosswalks
        .Select(x => new CrossingsResult
        {
            ...
        }).ToList();
    foreach (var crosswalk in crosswalks)
    {
        crosswalk.SId = GetSId(d, _sequenceName);
    }
    return crosswalks;

但我希望调用Inside Select的方法不使用for循环