Add upsert merge strategy
#1466
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dlt/common/destination/reference.py
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| " dlt will fall back to `append` for this table." | ||
| ) | ||
| elif table.get("x-merge-strategy") == "upsert": | ||
| if self.config.destination_name not in ("postgres", "snowflake"): |
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Should we add a supported_merge_strategies destination capability?
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yes - if you at some point (as early as possible ie. when passing data to normalizer when we must have destination capabilities) are able to issue a warning and say which strategy will be used instead.
same thing with replace strategies (we have 3 afaik)
also if you want to do it: we do not even store which write dispositions are supported. so maybe this is a separate ticket :)
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- added
supported_merge_strategiescapability and configured it for all SQL destinations - added
_verify_destination_capabilitiesthat checks configured merge strategy against supported merge strategies- raises error if not supported
- (I know you suggested falling back to a supported strategy and issueing a warning instead, but I'm not a fan of that approach. Will of course change it if that's how we do things in
dlt, but wanted to challenge it first.)
- (I know you suggested falling back to a supported strategy and issueing a warning instead, but I'm not a fan of that approach. Will of course change it if that's how we do things in
- called right before
normalizestep — is that the right place?
- raises error if not supported
I can create a separate ticket for supported replace strategies and supported write dispositions capabilities.
dlt/destinations/sql_jobs.py
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| # generate statements for child tables if they exist | ||
| child_tables = table_chain[1:] | ||
| if child_tables: | ||
| root_row_key = escape_id("_dlt_id") |
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Should the row id be marked with a new hint (other than unique) to prevent hard-coding _dlt_id?
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why not unique? technically you just need a unique column to delete / merge child tables correctly. delete-insert does that, right?
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You need the root key to delete from child tables, because you check if the root key is present in the staging root table (lines 606 and 623 in sql_jobs.py).
If I understand correctly, the root key is always _dlt_id, not an arbitrary unique column.
delete-insert indeed uses the unique column hint instead of hard-coding _dlt_id, but that seems wrong to me.
Do we have a test case for the merge disposition with an arbitrary unique key? Maybe the tests pass because in practice the unique hint always resolves to _dlt_id in all our cases.
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no, we do not have such test case. what I want to achieve here is that we rely on annotations, not on column names.
_dlt_idis annotated asuniqueby a standard schemaroot_keyis a also an annotation, not a hardcoded field
relational.pyadds config for each table withmergewrite disposition:
"propagation": {
"tables": {
table_name: {
TColumnName(self.c_dlt_id): TColumnName(self.c_dlt_root_id)
}
}
}
which will propagate _dlt_id from root to each child table as _dlt_root_id and
self.schema._merge_hints(
{
"not_null": [
TSimpleRegex(self.c_dlt_id),
TSimpleRegex(self.c_dlt_root_id),
TSimpleRegex(self.c_dlt_parent_id),
TSimpleRegex(self.c_dlt_list_idx),
TSimpleRegex(self.c_dlt_load_id),
],
"foreign_key": [TSimpleRegex(self.c_dlt_parent_id)],
"root_key": [TSimpleRegex(self.c_dlt_root_id)],
"unique": [TSimpleRegex(self.c_dlt_id)],
},
normalize_identifiers=False, # already normalized
)
makes sure that hints are applied. this is quite old version of dlt and we'll reimplement it. but high level mechanism (we rely on annotations, not names) is good
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this looks good, is short and clean. important info
- I must merge allows naming conventions to be changed #998 - there all column names are abstracted away etc. your PR will generate a lot of conflict and it will be way easier to merge it after that
- for later: it would be cool if users can request dlt id type for append/replace as well - ie to just use content or primary key (deterministic) hash
- what happens if input data is not deduplicated? so we have several values with the same primary key?
delete-insertis deduplicating input data. see what happens in your case
dlt/common/destination/reference.py
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| " dlt will fall back to `append` for this table." | ||
| ) | ||
| elif table.get("x-merge-strategy") == "upsert": | ||
| if self.config.destination_name not in ("postgres", "snowflake"): |
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yes - if you at some point (as early as possible ie. when passing data to normalizer when we must have destination capabilities) are able to issue a warning and say which strategy will be used instead.
same thing with replace strategies (we have 3 afaik)
also if you want to do it: we do not even store which write dispositions are supported. so maybe this is a separate ticket :)
| if row_hash: | ||
| row_id = self.get_row_hash(dict_row) # type: ignore[arg-type] | ||
| dict_row["_dlt_id"] = row_id | ||
| if row_id_type in ("key_hash", "row_hash"): |
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this logic must be moved to _add_row_id. I think the way we handle _dlt_id needs a little bit more work
- we have super simple bring your own
_dlt_id
row_id = flattened_row.get("_dlt_id", None)
if not row_id:
row_id = self._add_row_id(table, flattened_row, parent_row_id, pos, _r_lvl)
we should replace it with hint based method - if there's any unique column we use it for _dlt_id. that may be a separate ticket. but current "bring your own" must work and now you ignore it here
- we have many methods to generate
_dlt_idfor parent table: random, deterministic (primary key based) and content based (used by scd2). they way you do it now is good enough. in the future I'd like people to be able to pick the way dlt id is generated (ie viaItemsNormalizerConfiguration) - for child tables we always have deterministic
_dlt_id
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I have moved the logic to _add_row_id. Current "bring your own" (if I understand it correctly) should work now.
dlt/destinations/sql_jobs.py
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| # generate statements for child tables if they exist | ||
| child_tables = table_chain[1:] | ||
| if child_tables: | ||
| root_row_key = escape_id("_dlt_id") |
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why not unique? technically you just need a unique column to delete / merge child tables correctly. delete-insert does that, right?
…com/dlt-hub/dlt into feat/1129-add-upsert-merge-strategy
…mplement any of the defined merge strategies
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@rudolfix I addressed your comments. Can you review?
See "Note 1" in the PR description. |
rudolfix
added
the
sprint
…-add-upsert-merge-strategy
| assert "primary_key" in r._hints | ||
| assert "merge_key" in r._hints | ||
| p.run(r()) | ||
| assert ( |
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This assertion fails on CI because capsys.readouterr().err is an empty string there. It does work on my local machine. Any idea on how to best test warning logs?
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OK I have no idea. maybe the log is routed to stdout on CI? but I doubt that, or the test is really not passing
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Commented out the test for now so this doesn't block progress: 0f641e4
dlt/extract/hints.py
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| dict_["x-merge-strategy"] = DEFAULT_MERGE_STRATEGY | ||
| if "strategy" in mddict: | ||
| if mddict["strategy"] not in MERGE_STRATEGIES: | ||
| raise ValueError( |
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Is this the right way/place to do user input validation?
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good point. probably not. all hints are applied via apply_hints method which calls _set_hints at the end. the validation should happen there. I think it makes sense to move those checks. there's a little bit of validation already done in _set_hints
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Moved it to _set_hints in 479e52a
rudolfix
removed
the
sprint
…-add-upsert-merge-strategy
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This is really good and test coverage is sufficient. I had a few remarks regarding using hardcoded column names vs annotation but it looks mostly fixed now.
other things are minor
we also lack some docs but can go to the next PR. up to you
again - sorry for the big merge and conflicts - you'll have a few more places to fix when you merge current devel - but way less than last time
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| @staticmethod | ||
| @lru_cache(maxsize=None) | ||
| def _get_primary_key(schema: Schema, table_name: str) -> List[str]: |
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here's one detail: we may be dealing with non-existing table that nevertheless gets primary key from schema hints. (data comes first, then we detect the schema - so to be fully correct we'd need to use flattened data to predict if any primary key will be detected on it)
I looked at our code and this will significantly slow us down, make caching harder etc. so let's ignore it for now.
| elif merge_strategy == "scd2": | ||
| if ( | ||
| schema.get_table(table_name)["columns"] | ||
| .get("_dlt_id", {}) |
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maybe use get_columns_names_with_prop to look for "x-row-version" directly?
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I adjusted in 0d84e6d
dlt/destinations/sql_client.py
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| @@ -173,6 +173,12 @@ def make_qualified_table_name_path( | |||
| path.append(table_name) | |||
| return path | |||
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| def get_qualified_table_names(self, table_name: str, escape: bool = True) -> Tuple[str, str]: | |||
| """Returns qualified names for table and corresponding staging table as tuple.""" | |||
| with self.with_staging_dataset(staging=True): | |||
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I removed stagingflag fromwith_staging_dataset. it is in devel` now
dlt/extract/hints.py
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| dict_["x-merge-strategy"] = DEFAULT_MERGE_STRATEGY | ||
| if "strategy" in mddict: | ||
| if mddict["strategy"] not in MERGE_STRATEGIES: | ||
| raise ValueError( |
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good point. probably not. all hints are applied via apply_hints method which calls _set_hints at the end. the validation should happen there. I think it makes sense to move those checks. there's a little bit of validation already done in _set_hints
| assert "primary_key" in r._hints | ||
| assert "merge_key" in r._hints | ||
| p.run(r()) | ||
| assert ( |
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OK I have no idea. maybe the log is routed to stdout on CI? but I doubt that, or the test is really not passing
| merge_strategy: TLoaderMergeStrategy, | ||
| destination: TDestination, | ||
| ) -> None: | ||
| if merge_strategy not in destination.capabilities().supported_merge_strategies: |
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this is good. but should be a part of destinations_configs filters. definitely a task for the future: if we add supported write disposiitons to the capabilities we'll be able to generate a lot of filters automatically
This reverts commit 17f2115.
Description
upsertprimary_key, should be unique (see note 1)_dlt_iddelete-insertstrategymerge_keypostgresandsnowflakedestinations (other destinations come in follow up PR)Note 1:
A primary key-based
_dlt_idrequires that the primary key is unique before going into thenormalizestep. Primary key-based deduplication in theloadstep, as we do in thedelete-insertmerge strategy, is not possible.Problems when primary key is not unique (i.e. it has duplicates):
UNIQUEconstraint on_dlt_idcolumn is violated (can be solved by not imposing the constraint)Related Issues
upsertmerge strategy #1129