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Mentioned the 767 bytes index limit and its solution #10055

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Mentioned the 767 bytes index limit and its solution
javiereguiluz Jul 12, 2018
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Minor tweak
javiereguiluz Jul 16, 2018
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10 changes: 10 additions & 0 deletions doctrine.rst
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Expand Up @@ -149,6 +149,15 @@ can automatically generate an empty ``test_project`` database for you:
support 4-byte unicode characters, and strings containing them will be
truncated. This is fixed by the `newer utf8mb4 character set`_.

.. caution::

MySQL sets a `limit of 767 bytes for the index key prefix`_. When using
``utf8mb4``, string columns with 255 character length surpass that limit.
This means that any column of type ``string`` and ``unique=true`` must
set its maximum ``length`` to ``190``. Otherwise, you'll see this error:
*"[PDOException] SQLSTATE[42000]: Syntax error or access violation:
1071 Specified key was too long; max key length is 767 bytes"*.

.. note::

If you want to use SQLite as your database, you need to set the path
Expand Down Expand Up @@ -838,3 +847,4 @@ Learn more
.. _`FrameworkExtraBundle documentation`: https://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/converters.html
.. _`newer utf8mb4 character set`: https://dev.mysql.com/doc/refman/5.5/en/charset-unicode-utf8mb4.html
.. _`Transactions and Concurrency`: http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/reference/transactions-and-concurrency.html
.. _`limit of 767 bytes for the index key prefix`: https://dev.mysql.com/doc/refman/5.6/en/innodb-restrictions.html