The following code snippet is an SQL Alchemy ORM table definition class.
class HtmlData(MyBase):
__tablename__ = 'html_data_table_name'
html_id: Mapped[int] = mapped_column(primary_key=True)
html_div: Mapped[str]
html_div_md5: Mapped[str]
If I run the create_all command from within Python code, this will create a table where the column html_div_md5 has the type varchar.
However, this is a varchar of unconstrained length.
This doesn’t make a huge amount of sense, since md5 hashes are all 128 bits in length, or 16 bytes long.
It is likely that specifying the length to be fixed to be 16 bytes will improve performance, and it will almost certainly reduce the required data storage size. (I might be able to test this.)
How can I fix the length of html_div_md5 using the Mapped[str] syntax?
The solution is to use the SQL Alchemy String datatype, which can be imported and used as follows.
from sqlalchemy import String
class HtmlData(MyBase):
__tablename__ = 'html_data_table_name'
html_id: Mapped[int] = mapped_column(primary_key=True)
html_div: Mapped[str]
html_div_md5: Mapped[str] = mapped_column(String(16))