- SQLAlchemy Tutorial
- SQLAlchemy - Home
- SQLAlchemy - Introduction
- SQLAlchemy Core
- Expression Language
- Connecting to Database
- Creating Table
- SQL Expressions
- Executing Expression
- Selecting Rows
- Using Textual SQL
- Using Aliases
- Using UPDATE Expression
- Using DELETE Expression
- Using Multiple Tables
- Using Multiple Table Updates
- Parameter-Ordered Updates
- Multiple Table Deletes
- Using Joins
- Using Conjunctions
- Using Functions
- Using Set Operations
- SQLAlchemy ORM
- Declaring Mapping
- Creating Session
- Adding Objects
- Using Query
- Updating Objects
- Applying Filter
- Filter Operators
- Returning List and Scalars
- Textual SQL
- Building Relationship
- Working with Related Objects
- Working with Joins
- Common Relationship Operators
- Eager Loading
- Deleting Related Objects
- Many to Many Relationships
- Dialects
- SQLAlchemy Useful Resources
- SQLAlchemy - Quick Guide
- SQLAlchemy - Useful Resources
- SQLAlchemy - Discussion
SQLAlchemy ORM - Textual SQL
Earlier, textual SQL using text() function has been explained from the perspective of core expression language of SQLAlchemy. Now we shall discuss it from ORM point of view.
Literal strings can be used flexibly with Query object by specifying their use with the text() construct. Most applicable methods accept it. For example, filter() and order_by().
In the example given below, the filter() method translates the string “id<3” to the WHERE id<3
from sqlalchemy import text
for cust in session.query(Customers).filter(text("id<3")):
print(cust.name)
The raw SQL expression generated shows conversion of filter to WHERE clause with the code illustrated below −
SELECT customers.id AS customers_id, customers.name AS customers_name, customers.address AS customers_address, customers.email AS customers_email FROM customers WHERE id<3
From our sample data in Customers table, two rows will be selected and name column will be printed as follows −
Ravi Kumar Komal Pande
To specify bind parameters with string-based SQL, use a colon,and to specify the values, use the params() method.
cust = session.query(Customers).filter(text("id = :value")).params(value = 1).one()
The effective SQL displayed on Python console will be as given below −
SELECT customers.id AS customers_id, customers.name AS customers_name, customers.address AS customers_address, customers.email AS customers_email FROM customers WHERE id = ?
To use an entirely string-based statement, a text() construct representing a complete statement can be passed to from_statement().
session.query(Customers).from_statement(text("SELECT * FROM customers")).all()
The result of above code will be a basic SELECT statement as given below −
SELECT * FROM customers
Obviously, all records in customers table will be selected.
The text() construct allows us to link its textual SQL to Core or ORM-mapped column expressions positionally. We can achieve this by passing column expressions as positional arguments to the TextClause.columns() method.
stmt = text("SELECT name, id, name, address, email FROM customers")
stmt = stmt.columns(Customers.id, Customers.name)
session.query(Customers.id, Customers.name).from_statement(stmt).all()
The id and name columns of all rows will be selected even though the SQLite engine executes following expression generated by above code shows all columns in text() method −
SELECT name, id, name, address, email FROM customers