SQLAlchemy - 在 postgresql 中执行批量更新插入(如果存在，更新，否则插入) [英] SQLAlchemy - performing a bulk upsert (if exists, update, else insert) in postgresql

问题描述

我正在尝试使用 SQLAlchemy 模块(而不是 SQL！)在 python 中编写批量更新插入.

I am trying to write a bulk upsert in python using the SQLAlchemy module (not in SQL!).

我在 SQLAlchemy 添加时收到以下错误:

I am getting the following error on a SQLAlchemy add:

sqlalchemy.exc.IntegrityError: (IntegrityError) duplicate key value violates unique constraint "posts_pkey"
DETAIL:  Key (id)=(TEST1234) already exists.

我有一个名为 posts 的表，在 id 列上有一个主键.

I have a table called posts with a primary key on the id column.

在这个例子中，我已经在数据库中有一行 id=TEST1234.当我尝试 db.session.add() 将 id 设置为 TEST1234 的新帖子对象时，出现上述错误.我的印象是，如果主键已经存在，记录就会更新.

In this example, I already have a row in the db with id=TEST1234. When I attempt to db.session.add() a new posts object with the id set to TEST1234, I get the error above. I was under the impression that if the primary key already exists, the record would get updated.

如何仅基于主键使用 Flask-SQLAlchemy 进行更新插入?有没有简单的解决方案?

如果没有，我总是可以检查并删除任何具有匹配 id 的记录，然后插入新记录，但这对于我的情况来说似乎很昂贵，我不希望有很多更新.

If there is not, I can always check for and delete any record with a matching id, and then insert the new record, but that seems expensive for my situation, where I do not expect many updates.

推荐答案

SQLAlchemy 中有一个 upsert-esque 操作:

There is an upsert-esque operation in SQLAlchemy:

db.session.merge()

找到这个命令后，我就可以执行upsert了，但值得一提的是，这个操作对于批量upsert"来说很慢.

After I found this command, I was able to perform upserts, but it is worth mentioning that this operation is slow for a bulk "upsert".

另一种方法是获取您要更新插入的主键的列表，并查询数据库以查找任何匹配的 ID:

The alternative is to get a list of the primary keys you would like to upsert, and query the database for any matching ids:

# Imagine that post1, post5, and post1000 are posts objects with ids 1, 5 and 1000 respectively
# The goal is to "upsert" these posts.
# we initialize a dict which maps id to the post object

my_new_posts = {1: post1, 5: post5, 1000: post1000} 

for each in posts.query.filter(posts.id.in_(my_new_posts.keys())).all():
    # Only merge those posts which already exist in the database
    db.session.merge(my_new_posts.pop(each.id))

# Only add those posts which did not exist in the database 
db.session.add_all(my_new_posts.values())

# Now we commit our modifications (merges) and inserts (adds) to the database!
db.session.commit()

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