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<col class="field-body" />
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<tbody valign="top">
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<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple">
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<li><strong>shard_chooser</strong> – A callable which, passed a Mapper, a mapped instance, and possibly a
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SQL clause, returns a shard ID. This id may be based off of the
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attributes present within the object, or on some round-robin
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scheme. If the scheme is based on a selection, it should set
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whatever state on the instance to mark it in the future as
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<li><strong>shard_chooser</strong> – A callable which, passed a Mapper, a mapped
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instance, and possibly a SQL clause, returns a shard ID. This id
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may be based off of the attributes present within the object, or on
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some round-robin scheme. If the scheme is based on a selection, it
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should set whatever state on the instance to mark it in the future as
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participating in that shard.</li>
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<li><strong>id_chooser</strong> – A callable, passed a query and a tuple of identity values, which
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should return a list of shard ids where the ID might reside. The
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databases will be queried in the order of this listing.</li>
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<li><strong>query_chooser</strong> – For a given Query, returns the list of shard_ids where the query
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should be issued. Results from all shards returned will be combined
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together into a single listing.</li>
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<li><strong>shards</strong> – A dictionary of string shard names to <a class="reference internal" href="../../core/connections.html#sqlalchemy.engine.base.Engine" title="sqlalchemy.engine.base.Engine"><tt class="xref py py-class docutils literal"><span class="pre">Engine</span></tt></a>
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<li><strong>id_chooser</strong> – A callable, passed a query and a tuple of identity
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values, which should return a list of shard ids where the ID might
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reside. The databases will be queried in the order of this listing.</li>
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<li><strong>query_chooser</strong> – For a given Query, returns the list of shard_ids
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where the query should be issued. Results from all shards returned
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will be combined together into a single listing.</li>
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<li><strong>shards</strong> – A dictionary of string shard names
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to <a class="reference internal" href="../../core/connections.html#sqlalchemy.engine.Engine" title="sqlalchemy.engine.Engine"><tt class="xref py py-class docutils literal"><span class="pre">Engine</span></tt></a> objects.</li>
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