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H-Shay 2023-04-28 17:59:58 +00:00
parent e422e054d4
commit 7f8069d98a
4 changed files with 2 additions and 60 deletions
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29
develop/development/database_schema.html
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@ -275,39 +275,10 @@ def run_upgrade(
<h2 id="boolean-columns"><a class="header" href="#boolean-columns">Boolean columns</a></h2>
<p>Boolean columns require special treatment, since SQLite treats booleans the
same as integers.</p>
<p>There are three separate aspects to this:</p>
<ul>
<li>
<p>Any new boolean column must be added to the <code>BOOLEAN_COLUMNS</code> list in
<code>synapse/_scripts/synapse_port_db.py</code>. This tells the port script to cast
the integer value from SQLite to a boolean before writing the value to the
postgres database.</p>
</li>
<li>
<p>Before SQLite 3.23, <code>TRUE</code> and <code>FALSE</code> were not recognised as constants by
SQLite, and the <code>IS [NOT] TRUE</code>/<code>IS [NOT] FALSE</code> operators were not
supported. This makes it necessary to avoid using <code>TRUE</code> and <code>FALSE</code>
constants in SQL commands.</p>
<p>For example, to insert a <code>TRUE</code> value into the database, write:</p>
<pre><code class="language-python">txn.execute(&quot;INSERT INTO tbl(col) VALUES (?)&quot;, (True, ))
</code></pre>
</li>
<li>
<p>Default values for new boolean columns present a particular
difficulty. Generally it is best to create separate schema files for
Postgres and SQLite. For example:</p>
<pre><code class="language-sql"># in 00delta.sql.postgres:
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT FALSE;
</code></pre>
<pre><code class="language-sql"># in 00delta.sql.sqlite:
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT 0;
</code></pre>
<p>Note that there is a particularly insidious failure mode here: the Postgres
flavour will be accepted by SQLite 3.22, but will give a column whose
default value is the <strong>string</strong> <code>&quot;FALSE&quot;</code> - which, when cast back to a boolean
in Python, evaluates to <code>True</code>.</p>
</li>
</ul>
<h2 id="event_id-global-uniqueness"><a class="header" href="#event_id-global-uniqueness"><code>event_id</code> global uniqueness</a></h2>
<p><code>event_id</code>'s can be considered globally unique although there has been a lot of
debate on this topic in places like

29
develop/print.html
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@ -16564,39 +16564,10 @@ def run_upgrade(
<h2 id="boolean-columns"><a class="header" href="#boolean-columns">Boolean columns</a></h2>
<p>Boolean columns require special treatment, since SQLite treats booleans the
same as integers.</p>
<p>There are three separate aspects to this:</p>
<ul>
<li>
<p>Any new boolean column must be added to the <code>BOOLEAN_COLUMNS</code> list in
<code>synapse/_scripts/synapse_port_db.py</code>. This tells the port script to cast
the integer value from SQLite to a boolean before writing the value to the
postgres database.</p>
</li>
<li>
<p>Before SQLite 3.23, <code>TRUE</code> and <code>FALSE</code> were not recognised as constants by
SQLite, and the <code>IS [NOT] TRUE</code>/<code>IS [NOT] FALSE</code> operators were not
supported. This makes it necessary to avoid using <code>TRUE</code> and <code>FALSE</code>
constants in SQL commands.</p>
<p>For example, to insert a <code>TRUE</code> value into the database, write:</p>
<pre><code class="language-python">txn.execute(&quot;INSERT INTO tbl(col) VALUES (?)&quot;, (True, ))
</code></pre>
</li>
<li>
<p>Default values for new boolean columns present a particular
difficulty. Generally it is best to create separate schema files for
Postgres and SQLite. For example:</p>
<pre><code class="language-sql"># in 00delta.sql.postgres:
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT FALSE;
</code></pre>
<pre><code class="language-sql"># in 00delta.sql.sqlite:
ALTER TABLE tbl ADD COLUMN col BOOLEAN DEFAULT 0;
</code></pre>
<p>Note that there is a particularly insidious failure mode here: the Postgres
flavour will be accepted by SQLite 3.22, but will give a column whose
default value is the <strong>string</strong> <code>&quot;FALSE&quot;</code> - which, when cast back to a boolean
in Python, evaluates to <code>True</code>.</p>
</li>
</ul>
<h2 id="event_id-global-uniqueness"><a class="header" href="#event_id-global-uniqueness"><code>event_id</code> global uniqueness</a></h2>
<p><code>event_id</code>'s can be considered globally unique although there has been a lot of
debate on this topic in places like

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develop/searchindex.js
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develop/searchindex.json
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