Attribute names are now checked against DynamoDB-compatible length
limits. When exceeded, Alternator emits exception identical or similar
to the DDB one. It might be worth noting that DDB emits more than a
single kind of an exception string for some exceptions. The tests'
catch clauses handle all the observed kinds of messages from DynamoDB.
The validation differentiates between key and non-key attributes and
applies the limit accordingly.
AWS DDB raises exceptions with somewhat different contents when the
get request contains ProjectionExpression, so this case needed separate
treatment to emit the corresponding exception string. The
length-validating function was declared and defined in
expressions.hh/.cc respectively, because that's where the relevant
parsing happens.
** Tests
The following tests were validated when handling this issue:
test_limit_attribute_length_nonkey_good,
test_limit_attribute_length_nonkey_bad,
test_limit_attribute_length_key_good,
test_limit_attribute_length_key_bad,
test_limit_attribute_length_gsi_lsi_good,
test_limit_attribute_length_gsi_lsi_bad,
test_limit_attribute_length_gsi_lsi_projection_bad.
Some of the tests were expanded into being more granular. Namely, there
is a new test function
`test_limit_attribute_length_key_bad_incoherent_names`
which groups tests with too long attribute names in the case of
incorrect (incoherent) user requests.
Similarily, there is a new test function
`test_limit_attribute_length_gsi_lsi_bad_incoherent_names`
All the tests cover now each combination of the key/keys being too long.
Both the new fuctions contain tests that verify that ScyllaDB throws
length-related exceptions (instead of the coherency-related), similar
to what DynamoDB does.
The new test test_limit_gsiu_key_len_bad covers the case of too long
attribute name inside GlobalSecondaryIndexUpdates.
The new test test_limit_gsiu_key_len_bad_incoherent_names covers the
case of incorrect (incoherent) user requests containing too long
attribute names and GlobalSecondaryIndexUpdates.
test_limit_attribute_length_key_bad was found to have contaned an
illegal KeySchema structure.
Some of the tests were corrected their match clause.
All the tests are stripped of the xfail flag except
test_limit_attribute_length_key_bad, which has it changed since it
still fails due to Projection in GSI and LIS not implemented in Alternator.
The xfail now points to #5036.
Fixesscylladb/scylladb#9169Closesscylladb/scylladb#23097
The later includes the former and in addition to `seastar::format()`,
`print.hh` also provides helpers like `seastar::fprint()` and
`seastar::print()`, which are deprecated and not used by scylladb.
Previously, we include `seastar/core/print.hh` for using
`seastar::format()`. and in seastar 5b04939e, we extracted
`seastar::format()` into `seastar/core/format.hh`. this allows us
to include a much smaller header.
In this change, we just include `seastar/core/format.hh` in place of
`seastar/core/print.hh`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#21574
now that we are allowed to use C++23. we now have the luxury of using
`std::ranges::any_of`.
in this change, we replace `boost::algorithm::any_of` with
`std::ranges::any_of`
to reduce the dependency to boost for better maintainability, and
leverage standard library features for better long-term support.
this change is part of our ongoing effort to modernize our codebase
and reduce external dependencies where possible.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
before this change, we rely on `using namespace seastar` to use
`seastar::format()` without qualifying the `format()` with its
namespace. this works fine until we changed the parameter type
of format string `seastar::format()` from `const char*` to
`fmt::format_string<...>`. this change practically invited
`seastar::format()` to the club of `std::format()` and `fmt::format()`,
where all members accept a templated parameter as its `fmt`
parameter. and `seastar::format()` is not the best candidate anymore.
despite that argument-dependent lookup (ADT for short) favors the
function which is in the same namespace as its parameter, but
`using namespace` makes `seastar::format()` more competitive,
so both `std::format()` and `seastar::format()` are considered
as the condidates.
that is what is happening scylladb in quite a few caller sites of
`format()`, hence ADT is not able to tell which function the winner
in the name lookup:
```
/__w/scylladb/scylladb/mutation/mutation_fragment_stream_validator.cc:265:12: error: call to 'format' is ambiguous
265 | return format("{} ({}.{} {})", _name_view, s.ks_name(), s.cf_name(), s.id());
| ^~~~~~
/usr/bin/../lib/gcc/x86_64-redhat-linux/14/../../../../include/c++/14/format:4290:5: note: candidate function [with _Args = <const std::basic_string_view<char> &, const seastar::basic_sstring<char, unsigned int, 15> &, const seastar::basic_sstring<char, unsigned int, 15> &, const utils::tagged_uuid<table_id_tag> &>]
4290 | format(format_string<_Args...> __fmt, _Args&&... __args)
| ^
/__w/scylladb/scylladb/seastar/include/seastar/core/print.hh:143:1: note: candidate function [with A = <const std::basic_string_view<char> &, const seastar::basic_sstring<char, unsigned int, 15> &, const seastar::basic_sstring<char, unsigned int, 15> &, const utils::tagged_uuid<table_id_tag> &>]
143 | format(fmt::format_string<A...> fmt, A&&... a) {
| ^
```
in this change, we
change all `format()` to either `fmt::format()` or `seastar::format()`
with following rules:
- if the caller expects an `sstring` or `std::string_view`, change to
`seastar::format()`
- if the caller expects an `std::string`, change to `fmt::format()`.
because, `sstring::operator std::basic_string` would incur a deep
copy.
we will need another change to enable scylladb to compile with the
latest seastar. namely, to pass the format string as a templated
parameter down to helper functions which format their parameters.
to miminize the scope of this change, let's include that change when
bumping up the seastar submodule. as that change will depend on
the seastar change.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
in theory, std::result_of_t should have been removed in C++20. and
std::invoke_result_t is available since C++17. thanks to libstdc++,
the tree is compiling. but we should not rely on this.
so, in this change, we replace all `std::result_of_t` with
`std::invoke_result_t`. actually, clang + libstdc++ is already warning
us like:
```
In file included from /home/runner/work/scylladb/scylladb/multishard_mutation_query.cc:9:
In file included from /home/runner/work/scylladb/scylladb/schema/schema_registry.hh:11:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/unordered_map:38:
Warning: /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/12/type_traits:2624:5: warning: 'result_of<void (noop_compacted_fragments_consumer::*(noop_compacted_fragments_consumer &))()>' is deprecated: use 'std::invoke_result' instead [-Wdeprecated-declarations]
2624 | using result_of_t = typename result_of<_Tp>::type;
| ^
/home/runner/work/scylladb/scylladb/mutation/mutation_compactor.hh:518:43: note: in instantiation of template type alias 'result_of_t' requested here
518 | if constexpr (std::is_same_v<std::result_of_t<decltype(&GCConsumer::consume_end_of_stream)(GCConsumer&)>, void>) {
|
```
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18835
before this change, we rely on the default-generated fmt::formatter
created from operator<<, but fmt v10 dropped the default-generated
formatter.
in this change, we define formatters for `alternator::parsed::path`,
and drop its operator<<.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17458
DynamoDB limits of all expressions (ConditionExpression, UpdateExpression,
ProjectionExpression, FilterExpression, KeyConditionExpression) to just
4096 bytes. Until now, Alternator did not enforce this limit, and we had
an xfailing test showing this.
But it turns out that not enforcing this limit can be dangerous: The user
can pass arbitrarily-long and arbitrarily nested expressions, such as:
a<b and (a<b and (a<b and (a<b and (a<b and (a<b and (...))))))
or
(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((
and those can cause recursive algorithms in Alternator's parser and
later when applying expressions to recurse very deeply, overflow the
stack, and crash.
This patch includes new tests that demonstrate how Scylla crashes during
parsing before enforcing the 4096-byte length limit on expressions.
The patch then enforces this length limit, and these tests stop crashing.
We also verify that deeply-nested expressions shorter than the 4096-byte
limit are apparently short enough for our recursion ability, and work
as expected.
Unforuntately, running these tests many times showed that the 4096-byte
limit is not low enough to avoid all crashes so this patch needs to do
more:
The parsers created by ANTLR are recursive, and there is no way to limit
the depth of their recursion (i.e., nothing like YACC's YYMAXDEPTH).
Very deep recursion can overflow the stack and crash Scylla. After we
limited the length of expression strings to 4096 bytes this was *almost*
enough to prevent stack overflows. But unfortunetely the tests revealed
that even limited to 4096 bytes, the expression can sometimes recurse
too deeply: Consider the expression "((((((....((((" with 4000 parentheses.
To realize this is a syntax error, the parser needs to do a recursive
call 4000 times. Or worse - because of other Antlr limitations (see rants
in comments in expressions.g) it's actually 12000 recursive calls, and
each of these calls have a pretty large frame. In some cases, this
overflows the stack.
The solution used in this patch is not pretty, but works. We add to rules
in alternator/expressions.g that recurse (there are two of those - "value"
and "boolean_expression") an integer "depth" parameter, which we increase
when the rule recurses. Moreover, we add a so-called predicate
"{depth<MAX_DEPTH}?" that stops the parsing when this limit is reached.
When the parsing is stopped, the user will see a special kind of parse
error, saying "expression nested too deeply".
With this last modification to expressions.g, the tests for deeply-nested but
still-below-4096-bytes expressions
(test_limits.py::test_deeply_nested_expression_*) would not fail sporadically
as they did without it.
While adding the "expression nested too deeply" case, I also made the
general syntax-error reporting in Alternator nicer: It no longer prints
the internal "expression_syntax_error" type name (an exception type will
only be printed if some sort of unexpected exception happens), and it
prints the character position where the syntax error (or too deep
nested expression) was recognized.
Fixes#14473
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#14477
The DynamoDB documentation for the size() function claims that it only
works on paths (attribute names or references), but it actually works on
constants from the query (e.g., ":val") as well.
It turns out that Alternator supports this undocumented case already, but
gets the error path wrong: Usually, when size() is calculated on the data,
if the data has the wrong type of size() (e.g., an integer), the condition
simply doesn't match. But if the value comes from the query - it should
generate an error that the query is wrong - ValidationException.
This patch fixes this case, and also adds tests for it that pass on both
DynamoDB and Alternator (after this patch).
Fixes#14592
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#14593
when formatting the error message for `api_error::validation`, we
always include the caller in the error message, but in this case,
forgot to pass the `caller` to `seastar::format()`. if fmtlib
actually formats them, it would throw.
so let's pass `caller` to `seastar::format()`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#14589
data
We'll try to distinguish the case when data comes from the storage rather
than user reuqest. Such attribute can be used in expressions and
when it can't be decoded it should make expression evaluate as
false to simply exclude the row during filter query or scan.
Note that this change focuses on binary type, for other types we
may have some inconsistencies in the implementation.
Following the advice in the FIXME note, helper functions for parsing
expressions are now based on string views to avoid a few unnecessary
conversions to std::string.
Tests: unit(dev)
Closes#10013
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
The rjson::set() *sounds* like it can set any member of a JSON object
(i.e., map), but that's not true :-( It calls the RapidJson function
AddMember() so it can only add a member to an object which doesn't have
a member with the same name (i.e., key). If it is called with a key
that already has a value, the result may have two values for the same
key, which is ill-formed and can cause bugs like issue #9542.
So in this patch we begin by renaming rjson::set() and its variant to
rjson::add() - to suggest to its user that this function only adds
members, without checking if they already exist.
After this rename, I was left with dozens of calls to the set() functions
that need to changed to either add() - if we're sure that the object
cannot already have a member with the same name - or to replace() if
it might.
The vast majority of the set() calls were starting with an empty item
and adding members with fixed (string constant) names, so these can
be trivially changed to add().
It turns out that *all* other set() calls - except the one fixed in
issue #9542 - can also use add() because there are various "excuses"
why we know the member names will be unique. A typical example is
a map with column-name keys, where we know that the column names
are unique. I added comments in front of such non-obvious uses of
add() which are safe.
Almost all uses of rjson except a handful are in Alternator, so I
verified that all Alternator test cases continue to pass after this
patch.
Fixes#9583
Refs #9542
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20211104152540.48900-1-nyh@scylladb.com>
The list_concatenate() function was only used for UpdateExpression's
ADD operation, so we made it a static function in the source file where
it was used. In the next patch, we'll want to use it in another place
(AttributeUpdates' ADD operation), so let's move it to the same file
where similar functions for sets exist.
This patch is almost entirely a code move, but also makes one small
change: list_concatenate() used to throw an exception if one of the
arguments wasn't a list, but the text of this exception was specific to
UpdateExpression. So in the new version, we return a null value in this
case - and the caller checks for it and throws the right exception.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The base64 encoding/decoding functions will be used for serialization of
hint sync point descriptions. Base64 format is not specific to
Alternator, so it can be moved to utils.
DynamoDB limits the depth of a nested path in expressions (e.g. "a.b.c.d")
to 32 levels. This patch adds the same limit also to Alternator.
The exact value of this limit is less important (although it did make
sense to choose the same limit as DynamoDB does), but it's important
to have *some* limit: It's often convenient to handle paths with a
recursive algorithm, and if we allow unlimited path depth, it can
result in unlimited recursion depth, and a crash. Let's avoid this
possibility.
We detect the over-long path while building the parsed::path object
in the parser, and generate a parse error.
This patch also includes a test that verifies that both Alternator
and DynamoDB have the same 32-level nesting limit on paths.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch fully implements support for attribute paths (e.g. a.b.c, a.d[3])
for the ConditionExpression in conditional updates, and FilterExpression in
queries and scans. After this patch, all previously-xfailing tests in
test_projection_expression.py and test_filter_expression.py now pass.
The fix is simple: Both ConditionExpression and FilterExpression use the
function calculate_value() to calculate the value of the expression. When
this function calculates the value of a path, it mustn't just take the
top-level attribute - it needs to walk into the specific sub-object as
specified by the attribute path.
This is not the end of attribute path support, UpdateExpression and
ReturnValues are not yet fully supported. This will come in following
patches.
Refs #5024
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch fully implements support for attribute paths (e.g. a.b.c, a.d[3])
for the ProjectionExpression in the various operations where this parameter
is supported - GetItem, BatchGetItem, Query and Scan. After this patch, all
xfailing tests in test_projection_expression.py now pass.
In the previous patch we remembered in the "attrs_to_get" object not only
the top-level attributes to read from the table, but also how to filter
from it only the desired pieces of the nested document. In this patch we
add a filter() function to do this filtering, and call it in the right
places to post-process the JSON objects we read from the table.
We also had to fix reference resolution in paths to resolve all the
components of the path (e.g., #name1.#name2) and not just the top-level
attribute.
This is not the end of attribute path support, there are still other
expressions (ConditionExpression, UpdateExpression, FilterExpression,
ReturnValues) where they are not yet supported. This will come in following
patches.
Refs #5024
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The first condition expressions we implemented in Alternator were the old
"Expected" syntax of conditional updates. That implementation had some
specific assumptions on how it handles errors: For example, in the "LT"
operator in "Expected", the second operand is always part of the query, so
an error in it (e.g., an unsupported type) resulted it a ValidationException
error.
When we implemented ConditionExpression and FilterExpression, we wrongly
used the same functions check_compare(), check_BETWEEN(), etc., to implement
them. This results in some inaccurate error handling. The worst example is
what happens when you use a FilterExpression with an expression such as
"x < y" - this filter is supposed to silently skip items whose "x" and "y"
attributes have unsupported or different types, but in our implementation
a bad type (e.g., a list) for y resulted in a ValidationException which
aborted the entire scan! Interestingly, in once case (that of BEGINS_WITH)
we actually noticed the slightly different behavior needed and implemented
the same operator twice - with ugly code duplication. But in other operators
we missed this problem completely.
This patch first adds extensive tests of how the different expressions
(Expected, QueryFilter, FilterExpression, ConditionExpression) and the
different operators handle various input errors - unsupported types,
missing items, incompatible types, etc. Importantly, the tests demonstrate
that there is often different behavior depending on whether the bad
input comes from the query, or from the item. Some of the new tests
fail before this patch, but others pass and were useful to verify that
the patch doesn't break anything that already worked correctly previously.
As usual, all the tests pass on Cassandra.
Finally, this patch *fixes* all these problems. The comparison functions
like check_compare() and check_BETWEEN() now not only take the operands,
they also take booleans saying if each of the operands came from the
query or from an item. The old-syntax caller (Expected or QueryFilter)
always say that the first operand is from the item and the second is
from the query - but in the new-syntax caller (ConditionExpression or
FilterExpression) any or all of the operands can come from the query
and need verification.
The old duplicated code for check_BEGINS_WITH() - which a TODO to remove
it - is finally removed. Instead we use the same idea of passing booleans
saying if each of its operands came from an item or from the query.
Fixes#8043
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
We had a bug when a Query/Scan had both projection (ProjectionExpression
or AttributesToGet) and filtering (FilterExpression or Query/ScanFilter).
The problem was that projection left only the requested attributes, and
the filter might have needed - and not got - additional attributes.
The solution in this patch is to add the generated JSON item also
the extra attributes needed by filtering (if any), run the filter on
that, and only at the end remove the extra filtering attributes from
the item to be returned.
The two tests
test_query_filter.py::test_query_filter_and_attributes_to_get
test_filter_expression.py::test_filter_expression_and_projection_expression
Which failed before this patch now pass so we drop their "xfail" tag.
Fixes#6951.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
All the places in conditions.cc, expressions.cc and serialization.cc where
we constructed an api_error, we always used the ValidationException type
string, which the code repeated dozens of times.
This patch converts all these places to use the factory function
api_error::validation().
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
In a couple of places, where we already have a std::string_view, there
is no need to convert to to a std::string (which requires allocation).
One cool observation (by Piotr Sarna) is that map over std::string_view
is fine, when the strings in the map are always string constants.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The source file alternator/executor.cc has grown too much, reaching almost
4,000 lines. In this patch I move about 400 lines out of executor.cc:
1. Some functions related to serialization of sets and lists were moved to
serialization.cc,
2. Functions related to evaluating parsed expressions were moved to
expressions.cc.
The header file expressions_eval.hh was also removed - the calculate_value()
functions now live in expressions.cc, so we can just define them in
expressions.hh, no need for a separate header files.
This patch just moves code around. It doesn't make any functional changes.
Refs #5783.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch provides a complete implementation for the FilterExpression
parameter - the newer syntax for filtering the results of the Query or
Scan operations.
The implementation is pretty straightforward - we already added earlier
a result-filtering framework to Alternator, and used it for the older
filtering syntax - QuryFilter and ScanFilter. All we had to do now was
to run the FilterExpression (which has the same syntax as a
ConditionExpression) on each individual items. The previous cleanup
patches were important to reduce the friction of running these expressions
on the items.
After the previous patches fixing small esoteric bugs in a few expression
functions, with this patch *all* the tests in test_filter_expression.py
now pass, and so do the two FilterExpression tests in test_query.py and
test_scan.py. As far as I know (and of course minus any bugs we'll discover
later), this marks the FilterExpression feature complete.
Fixes#5038.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
In the DynamoDB API, expressions (e.g., ConditionExpression and many more)
may contain references to column names ("#name") or to values (":val")
given in a separate part of the request - ExpressionAttributeNames and
ExpressionAttributeValues respectively.
Before this patch, we resolved these references as part of the expression's
evaluation. This approach had two downsides:
1. It often misdiagnosed (both false negatives and false positives) cases
of unused names and values in expressions. We already had two xfailing
tests with examples - which pass after this patch. This patch also
adds two additional tests, which failed before this patch and pass
with it.
2. In one of the following patches we will add support for FilterExpression,
where the same expression is used repeatedly on many items. It is a waste
(as well as makes the code uglier) to resolve the same references again
and again each time the expression is evaluated. We should be able
to do it just once.
So this patch introduces an intermediate step between parsing and evaluating
an expression - "resolving" the expression. The new resolve_*() functions
modify the already parsed expression, replacing references to attribute
names and constant values by the actual names and values taken from the
request. The resolve_*() functions also keep track which references were
used, making it very easy to check (as DynamoDB does) if there are any
unused names or values, before starting the evaluation.
The interface of evaluate() functions become much simpler - they no longer
need to know the original request (which was previously needed for
ExpressionAttributeNames/Values), the table's schema (which was previously
needed only for some error checking), keep track of which references were
used. This simplification is helpful for using the expressions in contexts
where these things (request and schema) are no longer conveniently available,
namely in FilterExpression.
A small side-benefit of this patch is that it moves a bit of code, which
handled resolving of references in expressions, from executor.cc to
expressions.cc. This is just the first step in a bigger effort to
reduce the size of executor.cc by moving code to smaller source files.
There is no attempt in this patch to move as much code as we can.
We will move more code in a separate patch in this series.
Fixes#6572.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
We were not consistent about using '#include "foo.hh"' instead of
'#include <foo.hh>' for scylla's own headers. This patch fixes that
inconsistency and, to enforce it, changes the build to use -iquote
instead of -I to find those headers.
Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>
Message-Id: <20200608214208.110216-1-espindola@scylladb.com>
This patch adds support for the ConditionExpression parameter of the
item-writing operations in Alternator: PutItem, UpdateItem and DeleteItem.
We already supported conditional updates/put/delete using the "Expected"
parameter. The ConditionExpression parameter implemented here provides a
very similar feature, using a different - and also newer and more powerful -
syntax.
The implementation here reuses much of our existing expression-parsing
infrastructure. Unsurprisingly, ConditionExpression's syntax has much in
common with UpdateExpression which we already support) and also many of the
comparison functions already implemented for "Expected". However, it's still
quite a bit of new code, because of the many different comparisons, functions,
and syntax variations we need to support.
This patch also expands alternator-test/test_condition_expression.py with
a few additional corner cases discovered during the development of this
patch.
Almost all of the tests for this feature (35 out of 39) now pass.
Two tests still fail because we don't yet support nested attributes (this
is a missing feature across Alternator), and two tests fail because of minor
ideosyncracies in DynamoDB's error path that we chose not to duplicate
yet (but still remember the difference in the form of an xfailing test).
Fixes#5035
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The idiomatic way to use an std::variant depending the type holds is to use
std::visit. This modern API makes it unnecessary to write many boiler-plate
functions to test and cast the type of the variant, and makes it impossible
to forget one of the options. So in this patch we throw out the old ways,
and welcome the new.
Thanks to Piotr Sarna for the idea.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20190704205625.20300-1-nyh@scylladb.com>
DynamoDB has two similar parameters - AttributesToGet and
ProjectionExpression - which are supported by the GetItem, Scan and
Query operations. Until now we supported only the older AttributesToGet,
and this patch adds support to the newer ProjectionExpression.
Besides having a different syntax, the main difference between
AttributesToGet and ProjectionExpression is that the latter also
allows fetching only a specific nested attribute, e.g., a.b[3].c.
We do not support this feature yet, although it would not be
hard to add it: With our current data representation, it means
fetching the top-level attribute 'a', whose value is a JSON, and then
post-filtering it to take out only the '.b[3].c'. We'll do that
later.
This patch also adds more test cases to test_projection_expression.py.
All tests except three which check the nested attributes now pass,
and those three xfail (they succeed on DynamoDB, and fail as expected
on Alternator), reminding us what still needs to be done.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The DynamoDB protocol is based on JSON, and most DynamoDB requests describe
the operation and its parameters via JSON objects such as maps and lists.
However, in some types of requests an "expression" is passed as a single
string, and we need to parse this string. These cases include:
1. Attribute paths, such as "a[3].b.c", are used in projection
expressions as well as inside other expressions described below.
2. Condition expressions, such as "(NOT (a=b OR c=d)) AND e=f",
used in conditional updates, filters, and other places.
3. Update expressions, such as "SET #a.b = :x, c = :y DELETE d"
This patch introduces the framework to parse these expressions, and
an implementation of parsing update expressions. These update expressions
will be used in the UpdateItem operation in the next patch.
All these expression syntaxes are very simple: Most of them could be
parsed as regular expressions, or at most a simple hand-written lexical
analyzer and recursive-descent parser. Nevertheless, we decided to specify
these parsers in the same ANTLR3 language already used in the Scylla
project for parsing CQL, hopefully making these parsers easier to reason
about, and easier to change if needed - and reducing the amount of boiler-
plate code.
The parsing of update expressions is most complete except that in SET
actions, only the "path = value" form is supported and not yet forms
forms such as "path1 = path2" (which does read-before-write) or
"path1 = path1 + value" or "path = function(...)".
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
