[SQLAlchemy] synchronize_session参数详解

def _do_pre_synchronize(self): 2 query = self.query 3 session = query.session 4 context = query._compile_context() 5 select_stmt = context.statement.with_only_columns( 6 self.primary_table.primary_key) 7 self.matched_rows = session.execute( 8 select_stmt, 9 mapper=self.mapper, 10 params=query._params).fetchall()

<span style="font-family: verdana, Arial, Helvetica, sans-serif; font-size: 14px; line-height: 1.5;">　　在delete or update操作之后，将session的identity_map与前一步获取到的记录进行match，符合条件的就从session中删掉或更新。<br></span>

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;">def</span><span style="color: #000000;"> _do_post_synchronize(self):
</span><span style="color: #008080;"> 2</span>         session =<span style="color: #000000;"> self.query.session
</span><span style="color: #008080;"> 3</span>         target_mapper =<span style="color: #000000;"> self.query._mapper_zero()
</span><span style="color: #008080;"> 4</span>         <span style="color: #0000ff;">for</span> primary_key <span style="color: #0000ff;">in</span><span style="color: #000000;"> self.matched_rows:
</span><span style="color: #008080;"> 5</span>             <span style="color: #008000;">#</span><span style="color: #008000;"> TODO: inline this and call remove_newly_deleted</span>
<span style="color: #008080;"> 6</span>             <span style="color: #008000;">#</span><span style="color: #008000;"> once</span>
<span style="color: #008080;"> 7</span>             identity_key =<span style="color: #000000;"> target_mapper.identity_key_from_primary_key(
</span><span style="color: #008080;"> 8</span> <span style="color: #000000;">                list(primary_key))
</span><span style="color: #008080;"> 9</span>             <span style="color: #0000ff;">if</span> identity_key <span style="color: #0000ff;">in</span><span style="color: #000000;"> session.identity_map:
</span><span style="color: #008080;">10</span> <span style="color: #000000;">                session._remove_newly_deleted(
</span><span style="color: #008080;">11</span> <span style="color: #000000;">                    [attributes.instance_state(
</span><span style="color: #008080;">12</span> <span style="color: #000000;">                        session.identity_map[identity_key]
</span><span style="color: #008080;">13</span> <span style="color: #000000;">                    )]
</span><span style="color: #008080;">14</span>                 )

• ‘evaluate‘

　　　在delete or update操作之前，用query中的条件直接对session的identity_map中的objects进行eval操作，将符合条件的记录下来。

<span style="color: #008080;"> 1</span> <span style="color: #0000ff;">def</span><span style="color: #000000;"> _do_pre_synchronize(self):
</span><span style="color: #008080;"> 2</span>         query =<span style="color: #000000;"> self.query
</span><span style="color: #008080;"> 3</span>         target_cls =<span style="color: #000000;"> query._mapper_zero().class_
</span><span style="color: #008080;"> 4</span> 
<span style="color: #008080;"> 5</span>         <span style="color: #0000ff;">try</span><span style="color: #000000;">:
</span><span style="color: #008080;"> 6</span>             evaluator_compiler =<span style="color: #000000;"> evaluator.EvaluatorCompiler(target_cls)
</span><span style="color: #008080;"> 7</span>             <span style="color: #0000ff;">if</span> query.whereclause <span style="color: #0000ff;">is</span> <span style="color: #0000ff;">not</span><span style="color: #000000;"> None:
</span><span style="color: #008080;"> 8</span>                 eval_condition =<span style="color: #000000;"> evaluator_compiler.process(
</span><span style="color: #008080;"> 9</span> <span style="color: #000000;">                    query.whereclause)
</span><span style="color: #008080;">10</span>             <span style="color: #0000ff;">else</span><span style="color: #000000;">:
</span><span style="color: #008080;">11</span>                 <span style="color: #0000ff;">def</span><span style="color: #000000;"> eval_condition(obj):
</span><span style="color: #008080;">12</span>                     <span style="color: #0000ff;">return</span><span style="color: #000000;"> True
</span><span style="color: #008080;">13</span> 
<span style="color: #008080;">14</span> <span style="color: #000000;">            self._additional_evaluators(evaluator_compiler)
</span><span style="color: #008080;">15</span> 
<span style="color: #008080;">16</span>         <span style="color: #0000ff;">except</span><span style="color: #000000;"> evaluator.UnevaluatableError:
</span><span style="color: #008080;">17</span>             <span style="color: #0000ff;">raise</span><span style="color: #000000;"> sa_exc.InvalidRequestError(
</span><span style="color: #008080;">18</span>                 <span style="color: #800000;">"</span><span style="color: #800000;">Could not evaluate current criteria in Python. </span><span style="color: #800000;">"</span>
<span style="color: #008080;">19</span>                 <span style="color: #800000;">"</span><span style="color: #800000;">Specify ‘fetch‘ or False for the </span><span style="color: #800000;">"</span>
<span style="color: #008080;">20</span>                 <span style="color: #800000;">"</span><span style="color: #800000;">synchronize_session parameter.</span><span style="color: #800000;">"</span><span style="color: #000000;">)
</span><span style="color: #008080;">21</span> 
<span style="color: #008080;">22</span>         <span style="color: #008000;">#</span><span style="color: #008000;"> TODO: detect when the where clause is a trivial primary key match</span>
<span style="color: #008080;">23</span>         self.matched_objects =<span style="color: #000000;"> [
</span><span style="color: #008080;">24</span>             obj <span style="color: #0000ff;">for</span> (cls, pk), obj <span style="color: #0000ff;">in</span>
<span style="color: #008080;">25</span> <span style="color: #000000;">            query.session.identity_map.items()
</span><span style="color: #008080;">26</span>             <span style="color: #0000ff;">if</span> issubclass(cls, target_cls) <span style="color: #0000ff;">and</span>
<span style="color: #008080;">27</span>             eval_condition(obj)]

　　　在delete or update操作之后，将符合条件的记录删除或更新。

<span style="color: #008080;">1</span> <span style="color: #0000ff;">def</span><span style="color: #000000;"> _do_post_synchronize(self):
</span><span style="color: #008080;">2</span> <span style="color: #000000;">        self.query.session._remove_newly_deleted(
</span><span style="color: #008080;">3</span> <span style="color: #000000;">            [attributes.instance_state(obj)
</span><span style="color: #008080;">4</span>              <span style="color: #0000ff;">for</span> obj <span style="color: #0000ff;">in</span> self.matched_objects])

[SQLAlchemy] synchronize_session参数详解

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