Sqlalchemy get last X rows in order

Sqlalchemy get last X rows in order

To retrieve the last X rows from a table using SQLAlchemy while maintaining a specific order, you can use the order_by and limit clauses in your query. Here's how you can do it:

Assuming you have an SQLAlchemy model for your table, and you want to get the last X rows based on a specific column (e.g., timestamp) in descending order:

from sqlalchemy import create_engine, Column, Integer, String, DateTime from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker from sqlalchemy.sql import func # Create an SQLAlchemy engine and session engine = create_engine('sqlite:///your_database.db') # Replace with your database URL Session = sessionmaker(bind=engine) session = Session() # Define your SQLAlchemy model Base = declarative_base() class YourModel(Base): __tablename__ = 'your_table' id = Column(Integer, primary_key=True) name = Column(String) timestamp = Column(DateTime) # Query to get the last X rows in descending order of 'timestamp' x = 10 # Replace with the desired number of rows query = session.query(YourModel).order_by(YourModel.timestamp.desc()).limit(x) # Execute the query and retrieve the rows last_x_rows = query.all() # Print or process the retrieved rows for row in last_x_rows: print(row.id, row.name, row.timestamp)

In this code:

  1. We create an SQLAlchemy engine and session to interact with the database.

  2. We define the SQLAlchemy model YourModel to represent your table. Replace 'your_table', id, name, and timestamp with your actual table name and column names.

  3. We create a query using session.query() to select all rows from YourModel, ordering them by the timestamp column in descending order using order_by.

  4. We limit the query to retrieve only the last X rows using limit(x).

  5. We execute the query with query.all() to retrieve the rows.

  6. Finally, we iterate through the retrieved rows and print or process them as needed.

Adjust the values and column names in the code to match your specific table and requirements.

Examples

  1. SQLAlchemy Get Last X Rows with ORDER BY DESC and LIMIT

    • Description: This query explains how to get the last X rows in descending order and limit the result.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker Base = declarative_base() class User(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) name = Column(String) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 5 rows based on ID result = session.query(User).order_by(User.id.desc()).limit(5).all() for user in result: print(user.name)

  2. SQLAlchemy Get Last X Rows with OFFSET and LIMIT

    • Description: This query illustrates how to use OFFSET with LIMIT to get a subset of the last X rows.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker Base = declarative_base() class Log(Base): __tablename__ = 'logs' id = Column(Integer, primary_key=True) message = Column(String) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 10 rows, skipping the first 5 from the end result = session.query(Log).order_by(Log.id.desc()).offset(5).limit(10).all() for log in result: print(log.message)

  3. SQLAlchemy Get Last X Rows by Timestamp

    • Description: This query focuses on getting the last X rows based on a timestamp field.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String, DateTime from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker from datetime import datetime Base = declarative_base() class Event(Base): __tablename__ = 'events' id = Column(Integer, primary_key=True) name = Column(String) timestamp = Column(DateTime, default=datetime.utcnow) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 3 events by timestamp result = session.query(Event).order_by(Event.timestamp.desc()).limit(3).all() for event in result: print(event.name, event.timestamp)

  4. SQLAlchemy Get Last X Rows with Filtering and Limit

    • Description: This query shows how to apply a filter before retrieving the last X rows with a limit.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker Base = declarative_base() class Product(Base): __tablename__ = 'products' id = Column(Integer, primary_key=True) name = Column(String) category = Column(String) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 5 products in a specific category result = session.query(Product).filter(Product.category == "Electronics").order_by(Product.id.desc()).limit(5).all() for product in result: print(product.name)

  5. SQLAlchemy Get Last X Rows in a Complex Query

    • Description: This query demonstrates how to get the last X rows in a more complex query with joins and filtering.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String, ForeignKey from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker, relationship Base = declarative_base() class Customer(Base): __tablename__ = 'customers' id = Column(Integer, primary_key=True) name = Column(String) class Order(Base): __tablename__ = 'orders' id = Column(Integer, primary_key=True) customer_id = Column(Integer, ForeignKey('customers.id')) total = Column(Integer) customer = relationship("Customer", back_populates="orders") Customer.orders = relationship("Order", back_populates="customer") engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 3 orders for a specific customer result = session.query(Order).join(Order.customer).filter(Customer.name == "John").order_by(Order.id.desc()).limit(3).all() for order in result: print(order.total)

  6. SQLAlchemy Get Last X Rows with Group By and Order By

    • Description: This query demonstrates how to retrieve the last X rows in a grouped query with ORDER BY and LIMIT.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String, ForeignKey from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker, relationship Base = declarative_base() class Department(Base): __tablename__ = 'departments' id = Column(Integer, primary_key=True) name = Column(String) class Employee(Base): __tablename__ = 'employees' id = Column(Integer, primary_key=True) name = Column(String) department_id = Column(Integer, ForeignKey('departments.id')) department = relationship("Department") Department.employees = relationship("Employee", back_populates="department") engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 2 employees in each department result = session.query(Employee).group_by(Employee.department_id).order_by(Employee.id.desc()).limit(2).all() for employee in result: print(employee.name)

  7. SQLAlchemy Get Last X Rows with Pagination

    • Description: This query shows how to implement pagination to retrieve a specific "page" of results.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker Base = declarative_base() class Item(Base): __tablename__ = 'items' id = Column(Integer, primary_key=True) name = Column(String) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() page = 2 page_size = 5 offset = (page - 1) * page_size # Get the second page of the last 5 items result = session.query(Item).order_by(Item.id.desc()).offset(offset).limit(page_size).all() for item in result: print(item.name)

  8. SQLAlchemy Get Last X Rows with Multiple Order By Fields

    • Description: This query explains how to use multiple ORDER BY fields to retrieve the last X rows in a more specific order.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String, DateTime from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker from datetime import datetime Base = declarative_base() class Task(Base): __tablename__ = 'tasks' id = Column(Integer, primary key=True) description = Column(String) created_at = Column(DateTime, default=datetime.utcnow) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 5 tasks, ordered by creation date and ID result = session.query(Task).order_by(Task.created_at.desc(), Task.id.desc()).limit(5).all() for task in result: print(task.description, task.created_at)

  9. SQLAlchemy Get Last X Rows by Multiple Conditions

    • Description: This query demonstrates how to retrieve the last X rows with additional filtering conditions.
    • Code Example:
      from sqlalchemy import create_engine, Column, Integer, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import sessionmaker Base = declarative_base() class Message(Base): __tablename__ = 'messages' id = Column(Integer, primary key=True) content = Column(String) sender = Column(String) engine = create_engine("sqlite:///mydatabase.db") Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() # Get the last 3 messages from a specific sender result = session.query(Message).filter(Message.sender == "Alice").order_by(Message.id.desc()).limit(3).all() for message in result: print(message.content)

  10. SQLAlchemy Get Last X Rows with Custom Sorting

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