Working with SQLite Date and Timestamp Types in Python
If you’re working with date and timestamp values in Python, SQLite is a technology you might encounter. In this article, we’ll cover how to insert Python date/DateTime values into SQLite tables and how to read SQLite date/timestamp values in Python, and how to convert them into Python date/DateTime types.
Inserting Python Date/DateTime Value into SQLite Table
To insert a Python date/DateTime value into an SQLite table, you need to ensure that the destination column within the table is of the DATE or TIMESTAMP type. Here’s an example of how to insert a Python DateTime value into an SQLite table.
import sqlite3
from datetime import datetime
dbName = "Example.db"
tableName = "example_table"
dateValue = datetime.now()
# Connect to the database
connection = sqlite3.connect(dbName)
cursor = connection.cursor()
# Insert a record into the SQLite table
cursor.execute("INSERT INTO {} (timestamp_column) VALUES (?)".format(tableName), (dateValue,))
# Commit the transaction
connection.commit()
# Close the connection
connection.close()
The above example establishes a connection to an SQLite database, creates a cursor to query the database, and insert the converted Python DateTime value into the desired `timestamp_column` within the `example_table` table. Note how the DateTime value is converted into a Python tuple so that it can be added to the SQLite INSERT statement.
Reading SQLite Date/Timestamp Values in Python and Converting Them into Python Date/DateTime Types
There are two steps to read SQLite date/timestamp values; first, retrieving the value from the database, and second, converting it into a Python date/DateTime value. Here’s an example:
import sqlite3
from datetime import datetime
dbName = "Example.db"
tableName = "example_table"
# Connect to the database
connection = sqlite3.connect(dbName)
cursor = connection.cursor()
# Get the latest value of the date column
cursor.execute("SELECT timestamp_column FROM {} ORDER BY timestamp_column DESC LIMIT 1".format(tableName))
dbDateValue = cursor.fetchone()
# Convert the retrieved value to a datetime object
dateValue = datetime.strptime(dbDateValue[0], '%Y-%m-%d %H:%M:%S.%f')
# Close the connection
connection.close()
The above example establishes a connection to an SQLite database, retrieves the most recent `timestamp_column` value from the `example_table` table, and converts it into a Python DateTime value. Note the use of the `strptime()` method here to convert the retrieved SQLite date/timestamp string format into a Python DateTime object.
Ensuring Existence of an SQLite Table With a Timestamp Column for Data Retrieval/Insertion
Before performing any retrieval or insertion operations on an SQLite table, it is necessary to ensure that the table exists in the database and that the table has a column of the correct data type for the operation you are performing. Here’s an example of how to establish the existence of an SQLite table with a `timestamp_column` column.
import sqlite3
dbName = "Example.db"
tableName = "example_table"
# Connect to the database
connection = sqlite3.connect(dbName)
cursor = connection.cursor()
# Check for the existence of the table
cursor.execute("SELECT name FROM sqlite_master WHERE type='table' AND name=?", (tableName,))
tableExists = cursor.fetchone()
# Create the table if necessary
if not tableExists:
cursor.execute("CREATE TABLE {} (id INTEGER PRIMARY KEY, timestamp_column TIMESTAMP)".format(tableName))
connection.commit()
# Close the connection
connection.close()
The above example establishes a connection to an SQLite database, checks for the existence of the `example_table` table, and creates the table with a `timestamp_column` of the TIMESTAMP type if it does not exist. Note the use of the `name` field in the SELECT statement along with the `sqlite_master` table to check for the existence of the table.
Conclusion
In this article, we’ve covered how to insert Python date/DateTime values into SQLite tables, how to read SQLite date/timestamp values in Python and how to convert them into Python date/DateTime types, and how to ensure the existence of an SQLite table with the correct columns for data retrieval and insertion. These skills are essential if you’re working with date and timestamp data in a Python and SQLite environment.
Python Example to Insert/Retrieve DateTime from SQLite Table
When working with SQLite tables that contain DateTime values, you may encounter issues with how the sqlite3 module converts DateTime objects to string format. In this technical example, we will explore how to use the `detect_types` method in conjunction with `PARSE_DECLTYPES` and `PARSE_COLNAMES` arguments within the `connect` method to parse declared types and return DateTime objects.
We will also demonstrate how to retrieve the joining date from an SQLite table in `datetime.datetime` type after using `detect_types`. Default Behavior of sqlite3 Module: Converting DateTime Objects into String Format
By default, the SQLite module converts DateTime objects into string format before inserting them into an SQLite table.
This means that if we were to insert a Python DateTime object into an SQLite table, the value would be stored as a string rather than a DateTime object. The following code snippet demonstrates this behavior.
import sqlite3
from datetime import datetime
# Establish a connection to the SQLite database
conn = sqlite3.connect('example.db')
# Create a new table to hold dates
conn.execute('CREATE TABLE test(date_col TEXT)')
# Convert a datetime object to a string and insert it into the table
now = datetime.now()
conn.execute('INSERT INTO test(date_col) VALUES (?)', [now])
# Retrieve the date from the table
result = conn.execute('SELECT date_col FROM test').fetchone()
print(result)
When this code runs, the output will be something like `’2022-01-06 17:46:48.975445’`. Even though we inserted a DateTime object, we get a string back when we retrieve the value from the table.
Using detect_types with PARSE_DECLTYPES and PARSE_COLNAMES Arguments in `connect` Method to Parse Declared Type and Return DateTime Object
To return DateTime objects from an SQLite table, we can use the `detect_types` method in conjunction with `PARSE_DECLTYPES` and `PARSE_COLNAMES` arguments within the `connect` method. This will allow us to parse the declared types of columns and return the DateTime objects in their original format.
Here’s an example.
import sqlite3
from datetime import datetime
# Create a custom adapter to handle datetime objects
def adapt_datetime(datetime_obj):
return datetime_obj.isoformat(' ')
# Create a custom converter to convert sqlite column of 'timestamp' to datetime.datetime object
def convert_timestamp(timestamp):
return datetime.strptime(timestamp.decode('utf-8'), '%Y-%m-%d %H:%M:%S.%f')
# Register the adapter and converter with sqlite3 module
sqlite3.register_adapter(datetime, adapt_datetime)
sqlite3.register_converter("timestamp", convert_timestamp)
# Establish a connection to the SQLite database with detect_types enabled
conn = sqlite3.connect('example.db', detect_types=sqlite3.PARSE_DECLTYPES|sqlite3.PARSE_COLNAMES)
# Create a new table to hold dates
conn.execute('CREATE TABLE test(date_col TIMESTAMP)')
# Convert a datetime object to a string and insert it into the table
now = datetime.now()
conn.execute('INSERT INTO test(date_col) VALUES (?)', [now])
# Retrieve the date from the table
result = conn.execute('SELECT date_col FROM test').fetchone()[0]
print(type(result), result)
In the above code, we first create a custom adapter and converter to handle DateTime objects and the `timestamp` format used by SQLite. We then register them with the sqlite3 module.
Next, we establish a connection to the SQLite database with the `detect_types` argument set to `PARSE_DECLTYPES` and `PARSE_COLNAMES`. Note that we also change the SQL statement to create the `date_col` column to `TIMESTAMP` type, which will be used by SQLite to insert a timestamp and retrieve it back as a `datetime.datetime` object automatically.
Finally, we insert a DateTime object into the table and retrieve it back in its original format using `fetchone()` and index `[0]` to select the returned value.
Retrieving Joining Date in datetime.datetime Type after Using `detect_types`
Once `detect_types` has been enabled, we can use the `fetchall()` method to retrieve all rows from the SQLite table in their original format.
Here’s an example of how to retrieve the joining date of a user from an SQLite table in `datetime.datetime` format after enabling `detect_types`.
import sqlite3
import datetime
# Establish a connection to the SQLite database with detect_types enabled
conn = sqlite3.connect('example.db', detect_types=sqlite3.PARSE_DECLTYPES|sqlite3.PARSE_COLNAMES)
# Retrieve the joining date of a user
user_id = 1
result = conn.execute('SELECT joining_date FROM users WHERE id=?', [user_id]).fetchone()[0]
# Print the joining date in datetime format
print(type(result), result)
In this example, we retrieve the joining date of a user from an SQLite table with a column named `joining_date`. The `detect_types` argument enabled the SQLite module to convert the data from the `joining_date` column into its original format, `datetime.datetime`, allowing us to print the value in its proper format.
Conclusion
In this technical example, we’ve demonstrated how to use the `detect_types` method with `PARSE_DECLTYPES` and `PARSE_COLNAMES` arguments within the `connect` method to parse declared types and return DateTime objects. We’ve also shown how to retrieve the joining date from an SQLite table in `datetime.datetime` format after using `detect_types`.
These techniques can be used to make working with DateTime values in SQLite tables more seamless and effective. In conclusion, working with DateTime values in SQLite tables is essential for many Python developers.
The default behavior of the sqlite3 module may not be suitable for handling DateTime values, leading to issues when inserting or retrieving them. This article demonstrated how to use the `detect_types` method, with `PARSE_DECLTYPES` and `PARSE_COLNAMES` arguments within the `connect` method, to parse declared types and return DateTime objects.
We also showed how to retrieve a joining date from an SQLite table in `datetime.datetime` format using these techniques. By using these methods, developers can make working with DateTime values in SQLite tables more effective.
It is crucial to ensure the correct column types when inserting data and to properly retrieve data to ensure accurate data storage and manipulation.