prefetch_query
AlreadyLoadedNode
Bases: Node
Node that was already loaded in select statement
Source code in ormar\queryset\queries\prefetch_query.py
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extract_related_ids(column_name)
Extracts the selected column(s) values from own models. Those values are used to construct filter clauses and populate child models.
Parameters:
Name | Type | Description | Default |
---|---|---|---|
column_name |
str
|
names of the column(s) that holds the relation info |
required |
Returns:
Type | Description |
---|---|
List
|
List of extracted values of relation columns |
Source code in ormar\queryset\queries\prefetch_query.py
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load_data()
async
Triggers a data load in the child nodes
Source code in ormar\queryset\queries\prefetch_query.py
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reload_tree()
After data was loaded we reload whole tree from the bottom to include freshly loaded nodes
Source code in ormar\queryset\queries\prefetch_query.py
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LoadNode
Bases: Node
Nodes that actually need to be fetched from database in the prefetch query
Source code in ormar\queryset\queries\prefetch_query.py
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extract_related_ids(column_name)
Extracts the selected column(s) values from own models. Those values are used to construct filter clauses and populate child models.
Parameters:
Name | Type | Description | Default |
---|---|---|---|
column_names |
Union[str, List[str]]
|
names of the column(s) that holds the relation info |
required |
Returns:
Type | Description |
---|---|
List
|
List of extracted values of relation columns |
Source code in ormar\queryset\queries\prefetch_query.py
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load_data()
async
Ensures that at least primary key columns from current model are included in the query.
Gets the filter values from the parent model and runs the query.
Triggers a data load in child tasks.
Source code in ormar\queryset\queries\prefetch_query.py
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reload_tree()
Instantiates models from loaded database rows. Groups those instances by relation key for easy extract per parent. Triggers same for child nodes and then populates the parent node with own related models
Source code in ormar\queryset\queries\prefetch_query.py
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Node
Bases: ABC
Base Node use to build a query tree and divide job into already loaded models and the ones that still need to be fetched from database
Source code in ormar\queryset\queries\prefetch_query.py
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target_name: str
property
Return the name of the relation that is used to fetch excludes/includes from the excludable mixin as well as specifying the target to join in m2m relations
Returns:
Type | Description |
---|---|
str
|
name of the relation |
get_filter_for_prefetch()
Populates where clause with condition to return only models within the set of extracted ids. If there are no ids for relation the empty list is returned.
Returns:
Type | Description |
---|---|
List[sqlalchemy.sql.elements.TextClause]
|
list of filter clauses based on original models |
Source code in ormar\queryset\queries\prefetch_query.py
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PrefetchQuery
Query used to fetch related models in subsequent queries. Each model is fetched only ones by the name of the relation. That means that for each prefetch_related entry next query is issued to database.
Source code in ormar\queryset\queries\prefetch_query.py
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prefetch_related(models)
async
Main entry point for prefetch_query.
Receives list of already initialized parent models with all children from select_related already populated. Receives also list of row sql result rows as it's quicker to extract ids that way instead of calling each model.
Returns list with related models already prefetched and set.
Parameters:
Name | Type | Description | Default |
---|---|---|---|
models |
Sequence[Model]
|
list of already instantiated models from main query |
required |
rows |
List[sqlalchemy.engine.result.RowProxy]
|
row sql result of the main query before the prefetch |
required |
Returns:
Type | Description |
---|---|
List[Model]
|
list of models with children prefetched |
Source code in ormar\queryset\queries\prefetch_query.py
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RootNode
Bases: AlreadyLoadedNode
Root model Node from which both main and prefetch query originated
Source code in ormar\queryset\queries\prefetch_query.py
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UniqueList
Bases: list
Simple subclass of list that prevents the duplicates Cannot use set as the order is important
Source code in ormar\queryset\queries\prefetch_query.py
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