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Understanding the Difference Between server_default=func.now() and server_default=text('now()') in SQLAlchemy

# server_default=func.now() vs server_default=text('now()')

This article discusses the differences between using server_default=func.now() and server_default=text('now()') in SQLAlchemy to specify a server-side default value for a column in a database table. The article explains how each method generates the default value, and provides guidance on when to use one method over the other based on your specific use case and database requirements.

# Introduction

Both `server_default=func.now()` and `server_default=text('now()')` can be used to specify a server-side default value for a column in SQLAlchemy, but they differ in how the default value is generated.

# "server_default=func.now()"

  • It uses a SQLAlchemy function (`func.now()`) to generate the current date and time on the database server. This function generates a SQL expression that is specific to the database dialect being used. For example, for a PostgreSQL database, it generates the SQL expression `now()`, while for a MySQL database it generates `CURRENT_TIMESTAMP`.

# "server_default=text('now()')"

  • On the other hand, `server_default=text('now()')` uses a plain text SQL expression (`'now()'`) to generate the current date and time on the database server. This expression is not specific to any particular database dialect and must be written in a way that is compatible with all database backends. In this case, the `text` function is used to create a SQLAlchemy `TextClause` object that represents the SQL expression.

In summary:

server_default=func.now() generates a database-specific SQL expression using a SQLAlchemy function, while server_default=text('now()') generates a plain text SQL expression using a `TextClause` object. The choice between the two methods depends on your specific use case and which approach is better suited for your database and application requirements.

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