How to query json array in postgres with sqlalchemy?

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How to query json array in postgres with sqlalchemy?

2023-03-31 01:15| 来源: 网络整理| 查看: 265

SQLAlchemy is a popular SQL toolkit and Object-Relational Mapping (ORM) library for Python. It allows you to interact with databases in a Pythonic way without writing raw SQL statements. In recent years, JSON data types have been added to many relational databases, including Postgres. With the addition of JSON data types, it is now possible to store complex data structures, such as arrays, within a database.

Querying JSON arrays within a Postgres database can be challenging, especially if you are using SQLAlchemy. In this article, we will look at a few methods for querying JSON arrays using SQLAlchemy and Postgres.

Method 1: Using SQL Expressions

To query a JSON array in Postgres with SqlAlchemy using SQL expressions, you can use the any() function to match any element in the array. Here's an example:

from sqlalchemy import create_engine, Table, Column, Integer, String, JSON from sqlalchemy.sql import select, and_ import json engine = create_engine('postgresql://user:password@localhost/mydatabase') mytable = Table('mytable', metadata, Column('id', Integer, primary_key=True), Column('data', JSON) ) data = [{'name': 'John', 'age': 25}, {'name': 'Jane', 'age': 30}] engine.execute(mytable.insert().values(data=json.dumps(data))) query = select([mytable]).where(and_(mytable.c.data.any([{'name': 'John'}]), mytable.c.data.any([{'age': 25}]))) result = engine.execute(query) for row in result: print(row)

In this example, we create a table with a JSON column called data. We insert some data into the table, which is a list of dictionaries. We then query the table using the any() function to match any element in the data column that contains a dictionary with the keys name and age equal to 'John' and 25, respectively. The results are printed to the console.

Note that we use json.dumps() to convert the data to a JSON string before inserting it into the table, and we use json.loads() to convert the JSON string back to a Python object when we retrieve it from the table.

That's it! With this example, you should be able to query a JSON array in Postgres with SqlAlchemy using SQL expressions.

Method 2: Using SQLAlchemy JSON Functions

To query a JSON array in Postgres with SQLAlchemy, you can use the JSONB type and its associated functions. Here are the steps to do this:

Import the required modules: from sqlalchemy import create_engine, Table, Column, Integer, String, func from sqlalchemy.dialects.postgresql import JSONB from sqlalchemy.orm import sessionmaker Create a connection to the database: engine = create_engine('postgresql://user:password@host:port/database') Session = sessionmaker(bind=engine) session = Session() Define a table with a JSONB column: my_table = Table('my_table', metadata, Column('id', Integer, primary_key=True), Column('data', JSONB) ) Query the JSON array using the jsonb_array_elements function: query = session.query(my_table).\ filter(func.jsonb_array_elements(my_table.c.data['my_array']).\ astext == 'my_value')

In the above example, my_array is the name of the JSON array and my_value is the value you want to search for.

Execute the query and fetch the results: results = query.all()

You can also use other JSON functions like jsonb_extract_path_text to extract specific values from the JSON array.

query = session.query(my_table).\ filter(func.jsonb_extract_path_text(my_table.c.data, 'my_array', '0') == 'my_value')

In this example, 0 is the index of the element in the JSON array.

These are just a few examples of how you can query a JSON array in Postgres with SQLAlchemy using JSON functions. There are many more functions available, so be sure to check the SQLAlchemy and Postgres documentation for more information.

Method 3: Using SQLAlchemy Core

To query a JSON array in Postgres with SQLAlchemy Core, you can use the json_array_elements function to extract the elements of the array and then filter on those elements. Here is an example:

from sqlalchemy import create_engine, text engine = create_engine('postgresql://user:password@localhost/mydatabase') conn = engine.connect() query = text("SELECT * FROM mytable WHERE json_array_elements(mycolumn::json) = :value") result = conn.execute(query, value='{"key": "value"}') for row in result: print(row) conn.close()

In this example, we create an engine and a connection to our Postgres database. We then define a query using the text function and the json_array_elements function to extract the elements of the JSON array stored in the mycolumn column of the mytable table. We filter on the value of one of the elements using the = operator and the :value parameter. We then execute the query with the execute method of the connection object and iterate over the results with a for loop. Finally, we close the connection with the close method.

Note that the json_array_elements function returns a set of rows, one for each element of the array. To filter on a specific value, you need to use the = operator and the :value parameter with the WHERE clause.

I hope this helps you with your query!

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How to query json array in postgres with sqlalchemy?

How to query json array in postgres with sqlalchemy?

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