[BUG] 为什么add_vertices中的vid_field无法起作用，add_edges中的src_field和dst_field也是无法起效。

[yimijiu123]

Describe the bug
对于vid_field我的理解是，可以指定导入数据中的哪一列为点的ID列，用于后续载入边的对应索引属性。
在实际中，即使指定了vid_field的列，但是还是默认点数据集的第一列为ID列。比如：
`

sess = get_default_session()
#string点
graph = sess.g(oid_type="string")
id = np.array(['1', '2', '3', '4'])
idd = np.array(["a", "b", "c", "d"])
avg_score = np.array([11, 22, 23, 9])
v_data = np.transpose(np.vstack([idd,id, avg_score]))
df_student = pd.DataFrame(v_data, columns=["idd","id", "avg_score"])
src_id = np.array(['1', '2', '3', '1'])
dst_id = np.array(['2', '4', '2', '4'])
group_size = np.array([4,1,2,3])
e_data = np.transpose(np.vstack([src_id, dst_id, group_size]))
df_group = pd.DataFrame(e_data, columns=["src_id", "dst_id", "group_size"]).astype({"group_size": int})
graph = graph.add_vertices(df_student,label="student",vid_field="id")
graph=graph.add_edges(df_group,label="guide",src_label="student",dst_label="student")
pg = graph.project(vertices={"student": ["id"]}, edges={"guide": ["group_size"]})
`

输出结果为：

问题：

1. 可以看出vid_field="id"没有起效，也试过vid_field="1"、vid_field=id、vid_field=1，都不对。类似的，设置src_field=1，dst_field=0也不起效，只能交换边数据集的第一二列才可以实现交换出发点和目标点。
2. 不起效的原因是否是因为设置了：
   `

static constexpr int id_column = 0;
static constexpr int src_column = 0;
static constexpr int dst_column = 1;
static constexpr int edge_id_column = 2;
`

3. types_pb2.SRC_VID、types_pb2.SRC_LABEL、types_pb2.V_LABEL_ID、types_pb2.VID、types_pb2.LABEL与C++中的是否对应。比如：GetGid(fid_t fid, label_id_t label_id, oid_t oid, vid_t& gid)对应的是什么？为什么chunk.attr[types_pb2.VID].CopyFrom(utils.s_to_attr(str(self.vid_field)))？

[siyuan0322]

Thanks for reporting. It is a bug indeed. There was some logic to rearrange the column of the dataframe accordingly, but that piece of code maybe lost during massive refactor of loader 😢

These types_pb2.* is for carrying those meta information from python to C++, which is the CopyFrom statement is used for.

the GetGid is a method, the label_id, oid, gid is replaced by actually value of the vertex, the meaning is not related to the notions above.