我可以在MongoEngine文档中使用名为size的字段吗？

Question

我有一份文件：

List<float> getGradients(List<PointF> p)
{
    List<float> grads = new List<float>();
    for (int i = 0; i < p.Count - 1; i++)
    {
        float dx = p[i + 1].X - p[i].X;
        float dy = p[i + 1].Y - p[i].Y;
        if (dx == 0) grads.Add(dy == 0 ? 0 : dy > 0 ? 
            float.PositiveInfinity : float.NegativeInfinity);
        else grads.Add(dy / dx);
    }
    return grads;
}

List<float> getLengths(List<PointF> p)
{
    List<float> lengs = new List<float>();
    for (int i = 0; i < p.Count - 1; i++)
    {
        float dx = p[i + 1].X - p[i].X;
        float dy = p[i + 1].Y - p[i].Y;
        lengs.Add((float)Math.Sqrt(dy * dy + dx * dx));
    }
    return lengs;
}

List<float> getGaps(List<PointF> p, bool horizontal)
{
    List<float> gaps = new List<float>();
    for (int i = 0; i < p.Count - 1; i++)
    {
        float dx = p[i + 1].X - p[i].X;
        float dy = p[i + 1].Y - p[i].Y;
        gaps.Add(horizontal ? dx : dy);
    }
    return gaps;
}

List<int> getSigns(List<float> g)
{  
    return g.Select(x => x > 0 ? 1 : x == 0 ? 0 : -1).ToList();  
}

我可以使用

List<PointF> getBezz(List<PointF> points)
{
    List<PointF> bezz = new List<PointF>();
    int pMax = points.Count;

    List<float> hGaps = getGaps(points, true);
    List<float> vGaps = getGaps(points, false);
    List<float> grads = getGradients(points);
    List<float> lengs = getLengths(points);
    List<int> signs = getSigns(grads);

    PointF[] bezzA = new PointF[pMax * 3 - 2];

    // curve points
    for (int i = 0; i < pMax; i++) bezzA[i * 3] = points[i];

    // left control points
    for (int i = 1; i < pMax; i++)
    {
        float x = points[i].X - hGaps[i - 1] / 2f;
        float y = points[i].Y;
        if (i < pMax - 1 && signs[i - 1] == signs[i])
        {
            float m = (grads[i-1] + grads[i]) / 2f;
            y = points[i].Y - hGaps[i-1] / 2f * m * vGaps[i-1] / lengs[i-1];
        }
        bezzA[i * 3 - 1] = new PointF(x, y);
    }

    // right control points
    for (int i = 0; i < pMax - 1; i++)
    {
        float x = points[i].X + hGaps[i] / 2f;
        float y = points[i].Y;
        if (i > 0 && signs[i-1] == signs[i])
        {
            float m = (grads[i-1] + grads[i]) / 2f;
            y = points[i].Y + hGaps[i] / 2f * m  * vGaps[i] / lengs[i];
        }
        bezzA[i * 3 + 1] = new PointF(x, y);
    }
    return bezzA.ToList();
}

直到我尝试更新例如

class Hamburger(Document):
    size = IntField(default=0, required=True)

抛出此异常：

h = Hamburger()
h.size = 5
h.save()

可以使用名为size的字段的Document吗？有没有办法实现这个目标？