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        因为项目需要，用到了向量数据库Milvus，刚开始都没有遇到问题，直到一个表的主键是字符串（VARCHAR），在查询时刚好要以该主键作为查询条件，此时会出现异常，特此记录一下。

        记住，字符串查询，构建表达式时要加上单引号,比如下面的'{face_id}'，其实face_id本来就是一个字符串类型了，如果不加会出现如下的异常：
        # pymilvus.exceptions.MilvusException: <MilvusException: (code=65535, message=cannot parse expression: face_id == 2_0, error: invalid expression: face_id == 2_0)>

  具体看下面的代码（milvus_demo.py），其中exists()函数中构建查询表达式时做了特殊处理：

from pymilvus import connections, FieldSchema, CollectionSchema, DataType, Collection, utility, Partition
import time
from datetime import datetime
from typing import List#用于测试字符串查询的demo# MILVUS向量数据库地址
MILVUS_HOST_ONLINE = '127.0.0.1'
MILVUS_PORT = 19530# 检索时返回的匹配内容条数
VECTOR_SEARCH_TOP_K = 100class MilvusAvatar:# table_name 表名# partition_names  分区名,使用默认即可def __init__(self, mode, table_name, *, partition_names=["default"], threshold=1.1, client_timeout=3):self.table_name = table_nameself.partition_names = partition_namesself.host = MILVUS_HOST_ONLINEself.port = MILVUS_PORTself.client_timeout = client_timeoutself.threshold = thresholdself.sess: Collection = Noneself.partitions: List[Partition] = []self.top_k = VECTOR_SEARCH_TOP_Kself.search_params = {"metric_type": "L2", "params": {"nprobe": 256}}self.create_params = {"metric_type": "L2", "index_type": "IVF_FLAT", "params": {"nlist": 2048}}self.init()@propertydef fields(self):fields = [FieldSchema(name='face_id', dtype=DataType.VARCHAR, max_length=640, is_primary=True, auto_id = False),FieldSchema(name='media_id', dtype=DataType.INT64),FieldSchema(name='file_path', dtype=DataType.VARCHAR, max_length=640),  #原图片保存路径FieldSchema(name='name', dtype=DataType.VARCHAR, max_length=640),  #姓名FieldSchema(name='count', dtype=DataType.INT64),  #数量FieldSchema(name='save_path', dtype=DataType.VARCHAR, max_length=640),  #现保存的绝对路径，包含文件名FieldSchema(name='embedding', dtype=DataType.FLOAT_VECTOR, dim=512) ]return fields@propertydef output_fields(self):return ['face_id','media_id', 'file_path', 'name', 'count', 'save_path','embedding']def init(self):try:connections.connect(host=self.host, port=self.port)  # timeout=3 [cannot set]if utility.has_collection(self.table_name):self.sess = Collection(self.table_name)print(f'collection {self.table_name} exists')else:schema = CollectionSchema(self.fields)print(f'create collection {self.table_name} {schema}')self.sess = Collection(self.table_name, schema)self.sess.create_index(field_name="embedding", index_params=self.create_params)for index in self.partition_names:if not self.sess.has_partition(index):self.sess.create_partition(index)self.partitions = [Partition(self.sess, index) for index in self.partition_names]print('partitions: %s', self.partition_names)self.sess.load()except Exception as e:print(e)def query_expr_sync(self, expr, output_fields=None, client_timeout=None):if client_timeout is None:client_timeout = self.client_timeoutif not output_fields:output_fields = self.output_fieldsprint(f"MilvusAvatar query_expr_sync:{expr},output_fields:{output_fields}")print(f"MilvusAvatar num_entities:{self.sess.num_entities}")if self.sess.num_entities == 0:return []return  self.sess.query(partition_names=self.partition_names, output_fields=output_fields,expr=expr,_async= False,offset=0, limit=1000)# emb 为一个人脸特征向量def insert_avatar_sync(self, face_id, media_id, file_path, name, save_path, embedding):print(f'now insert_avatar {file_path}')print(f'now insert_avatar {file_path}')data = [[] for _ in range(len(self.sess.schema))] data[0].append(face_id)data[1].append(media_id)data[2].append(file_path)data[3].append(name)data[4].append(1)data[5].append(save_path)data[6].append(embedding)# 执行插入操作try:print('Inserting into Milvus...')self.partitions[0].insert(data=data)print(f'{file_path}')print(f"MilvusAvatar insert_avatar num_entities:{self.sess.num_entities}")except Exception as e:print(f'Milvus insert media_id:{media_id}, file_path:{file_path} failed: {e}')print(f'Milvus insert media_id:{media_id}, file_path:{file_path} failed: {e}')return Falsereturn True    # embs是一个数组def search_emb_sync(self, embs, expr='', top_k=None, client_timeout=None):if self.sess is None:return Noneif not top_k:top_k = self.top_kmilvus_records = self.sess.search(data=embs, partition_names=self.kb_ids, anns_field="embedding",param=self.search_params, limit=top_k,output_fields=self.output_fields, expr=expr, timeout=client_timeout)print(f"milvus_records:{milvus_records}")return milvus_records   def exists(self,face_id):print(f"exists:{face_id},{type(face_id)}")# 记住，字符串查询，构建表达式时要加上单引号,比如下面的'{face_id}'，其实face_id本来就是一个字符串类型了，如果不加会出现如下的异常：# pymilvus.exceptions.MilvusException: <MilvusException: (code=65535, message=cannot parse expression: face_id == 2_0, error: invalid expression: face_id == 2_0)>res = self.query_expr_sync(expr=f"face_id == '{face_id}'", output_fields=self.output_fields)#print(f"exists:{res},{len(res)}")if len(res) > 0: return Truereturn False# 修改照片数    def add_count(self, face_id):res = self.query_expr_sync(expr=f"face_id == '{face_id}'", output_fields=self.output_fields)self.sess.delete(expr=f"face_id == '{face_id}'")for result in res:media_id = result['media_id']file_path = result['file_path']name = result['name']count = int(result['count'])save_path = result['save_path']embedding = result['embedding']data = [[] for _ in range(len(self.sess.schema))] data[0].append(face_id)data[1].append(media_id)data[2].append(file_path)data[3].append(name)data[4].append(count + 1)data[5].append(save_path)data[6].append(embedding)    print(f"add_count face_id:{face_id},file_path:{file_path}, count:{count}")# 执行插入操作try:print('Inserting into Milvus...')self.partitions[0].insert(data=data)except Exception as e:print(f'Milvus insert media_id:{media_id}, file_path:{file_path} failed: {e}')return False                def delete_collection(self):print("delete_collection")self.sess.release()utility.drop_collection(self.table_name)def delete_partition(self, partition_name):print("delete_partition")part = Partition(self.sess, partition_name)part.release()self.sess.drop_partition(partition_name)def query_all(self,limit=None):res = self.sess.query(partition_names = self.partition_names, output_fields = ["face_id","media_id", "name", "count", "save_path"],expr= f"face_id != ''",_async = False,offset = 0, limit = None)print(res)return resif __name__ == "__main__":milvus_avatar= MilvusAvatar("local", "avatar", partition_names=["avatar"])media_id = 2index = 0face_id = f"{media_id}_{index}"file_path = "/home/data/bbh.jpg"save_path = "/home/data/bbh_avatar.jpg"embedding = [i/1000 for i in range(512)]milvus_avatar.insert_avatar_sync(face_id, media_id, file_path, "bbh", save_path, embedding)#result = milvus_avatar.query_all()#print(result)print(milvus_avatar.exists(face_id))

执行：python milvus_demo.py

如果是针对非字符串字段进行查询，则无需做上面的特殊处理。