Implement nullable reflected fields #38
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@@ -135,6 +135,59 @@ Supported field macros: | |
| | `sqlite_reflection::TimePoint` | `MEMBER_DATETIME(name)` | | ||
| | member function declaration | `FUNC(signature)` | | ||
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| ### Nullable fields | ||
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| Each field macro has a `_NULLABLE` variant (`MEMBER_INT_NULLABLE`, `MEMBER_REAL_NULLABLE`, | ||
| `MEMBER_TEXT_NULLABLE`, `MEMBER_BOOL_NULLABLE`, `MEMBER_DATETIME_NULLABLE`) declaring a field | ||
| that can represent the absence of a value. The field's type is `fcpp::optional_t<T>` from | ||
| [functional_cpp](https://github.com/jkalias/functional_cpp): under C++17 and later that is | ||
| literally `std::optional<T>`, so you get the standard type and API; under C++11 an equivalent | ||
| fallback with the core API (`has_value()`, `value()`, `operator*`/`->`, assignment from a value) | ||
| is used. | ||
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| ```c++ | ||
| #define REFLECTABLE Employee | ||
| #define FIELDS \ | ||
| MEMBER_TEXT(name) \ | ||
| MEMBER_TEXT_NULLABLE(middle_name) \ | ||
| MEMBER_REAL_NULLABLE(salary) | ||
| #include "reflection.h" | ||
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| Employee e; | ||
| e.name = L"Ada Lovelace"; // middle_name and salary stay unset | ||
| db->SaveAutoIncrement(e); // unset fields are stored as SQL NULL; e.id gets assigned | ||
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| const auto fetched = db->Fetch<Employee>(e.id); | ||
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There was a problem hiding this comment. Right — Generated by Claude Code |
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| if (fetched.salary.has_value()) { /* a real value was stored */ } | ||
| ``` | ||
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| Round-trip semantics: saving an unset nullable field binds SQL `NULL` | ||
| (`sqlite3_bind_null`), and fetching a `NULL` column hydrates the field back to the empty | ||
| state. A stored empty string and a stored zero are distinct from `NULL` and hydrate to a | ||
| *present* empty/zero value — absence and emptiness are no longer conflated. | ||
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| Two predicates cover nullness tests, since SQL's `= NULL` never matches: | ||
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| ```c++ | ||
| const auto is_unpaid = IsNull(&Employee::salary); | ||
| const auto unpaid = db->Fetch<Employee>(&is_unpaid); | ||
| const auto is_paid = IsNotNull(&Employee::salary); | ||
| const auto paid = db->Fetch<Employee>(&is_paid); | ||
| ``` | ||
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| Value predicates (`Equal`, `Like`, `GreaterThan`, `SmallerThanOrEqual`, ...) on a nullable | ||
| field compare against the contained value and take an optional as the comparison argument, | ||
| e.g. `Equal(&Employee::salary, fcpp::optional_t<double>(50000.0))` or | ||
| `GreaterThan(&Employee::salary, fcpp::optional_t<double>(40000.0))`. Passing an *empty* | ||
| optional to a value predicate throws `std::invalid_argument` — use `IsNull`/`IsNotNull` for | ||
| that instead. | ||
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| Non-nullable columns are now created with an explicit `NOT NULL` constraint, so the schema | ||
| enforces what the object model assumes. Because tables are created with | ||
| `CREATE TABLE IF NOT EXISTS`, this only affects newly created tables; pre-existing database | ||
| files keep their previous schema until migrated (the library has no migration layer yet) — | ||
| the same caveat that applies to `AUTOINCREMENT`. | ||
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| **Layout constraint.** Reflectable records must be simple, standard-layout structs: no base | ||
| classes, no virtual functions, no virtual/multiple inheritance. Member access is computed from | ||
| `offsetof`/pointer-to-member byte offsets, which are only well-defined for such types; a struct | ||
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@@ -42,6 +42,10 @@ struct REFLECTION_EXPORT SqlValue { | |
| bool bool_value; | ||
| double real_value; | ||
| std::string text_value; | ||
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| /// When true, the value represents SQL NULL (an unset nullable member) and is bound | ||
| /// via sqlite3_bind_null; the typed value members above are then meaningless | ||
| bool is_null; | ||
| }; | ||
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| /// The base class of all WHERE predicates used in SQLite queries | ||
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@@ -87,14 +91,25 @@ class REFLECTION_EXPORT QueryPredicate : public QueryPredicateBase { | |
| for (auto i = 0; i < record.member_metadata.size(); ++i) { | ||
| if (record.member_metadata[i].offset == offset) { | ||
| member_name_ = record.member_metadata[i].name; | ||
| auto value_address = (void*)&value; | ||
| if (record.member_metadata[i].nullable) { | ||
| // A value predicate on a nullable member compares against the contained | ||
| // value; an empty optional cannot be expressed as "= ?" in SQL (a bound | ||
| // NULL never matches), so demand IsNull()/IsNotNull() for that instead | ||
| value_address = NullableContainedValue(value_address, record.member_metadata[i].storage_class); | ||
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There was a problem hiding this comment. Agreed — Generated by Claude Code |
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| if (value_address == nullptr) { | ||
| throw std::invalid_argument("Value predicate on nullable member '" + member_name_ + | ||
| "' was given an empty optional; use IsNull()/IsNotNull() instead"); | ||
| } | ||
| } | ||
| value_ = value_retrieval(value_address, record.member_metadata[i].storage_class); | ||
| found = true; | ||
| break; | ||
| } | ||
| } | ||
| if (!found) { | ||
| throw std::runtime_error("No registered member of '" + record.name + | ||
| "' matches the given pointer-to-member (type id: " + typeid(T).name() + ")"); | ||
| } | ||
| } | ||
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@@ -111,6 +126,14 @@ class REFLECTION_EXPORT QueryPredicate : public QueryPredicateBase { | |
| /// to be type-erased, so that the header file is not bloated with unnecessary implementation details | ||
| virtual SqlValue GetSqlValue(void* v, SqliteStorageClass storage_class) const; | ||
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| private: | ||
| /// For a type-erased pointer to an fcpp::optional_t of the underlying type of the given | ||
| /// storage class, returns a pointer to the contained value, or nullptr when the optional | ||
| /// is empty. Lets the constructor above unwrap a nullable comparison value once, so the | ||
| /// virtual GetSqlValue overloads only ever see the plain underlying types | ||
| static void* NullableContainedValue(void* v, SqliteStorageClass storage_class); | ||
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| protected: | ||
| /// The symbol used for the comparison, for example "=" for equality | ||
| std::string symbol_; | ||
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@@ -177,6 +200,59 @@ class REFLECTION_EXPORT Like final : public QueryPredicate { | |
| SqlValue GetSqlValue(void* v, SqliteStorageClass storage_class) const override; | ||
| }; | ||
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| /// A predicate testing a column for the presence or absence of SQL NULL. Unlike the value | ||
| /// predicates it binds no value ("= NULL" never matches in SQL; nullness needs the dedicated | ||
| /// IS NULL / IS NOT NULL syntax), so it derives from QueryPredicateBase directly | ||
| class REFLECTION_EXPORT NullnessPredicate : public QueryPredicateBase { | ||
| public: | ||
| std::string Evaluate() const override; | ||
| std::vector<SqlValue> Bindings() const override; | ||
| QueryPredicateBase* Clone() const override; | ||
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| protected: | ||
| template <typename T, typename R> | ||
| NullnessPredicate(R T::* fn, const std::string& symbol) : symbol_(symbol) { | ||
| auto record = GetRecordFromTypeId(typeid(T).name()); | ||
| auto offset = OffsetFromStart(fn); | ||
| auto found = false; | ||
| for (auto i = 0; i < record.member_metadata.size(); ++i) { | ||
| if (record.member_metadata[i].offset == offset) { | ||
| member_name_ = record.member_metadata[i].name; | ||
| found = true; | ||
| break; | ||
| } | ||
| } | ||
| if (!found) { | ||
| throw std::runtime_error("No registered member of '" + record.name + | ||
| "' matches the given pointer-to-member (type id: " + typeid(T).name() + ")"); | ||
| } | ||
| } | ||
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| NullnessPredicate(const std::string& symbol, const std::string& member_name) | ||
| : symbol_(symbol), member_name_(member_name) {} | ||
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| /// The nullness test, either "IS NULL" or "IS NOT NULL" | ||
| std::string symbol_; | ||
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| /// The name of the tested member, as defined in source code | ||
| std::string member_name_; | ||
| }; | ||
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| /// A predicate matching rows whose column holds SQL NULL, i.e. rows whose | ||
| /// nullable member was saved in the unset/empty state | ||
| class REFLECTION_EXPORT IsNull final : public NullnessPredicate { | ||
| public: | ||
| template <typename T, typename R> | ||
| explicit IsNull(R T::* fn) : NullnessPredicate(fn, "IS NULL") {} | ||
| }; | ||
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| /// A predicate matching rows whose column holds a present (non-NULL) value | ||
| class REFLECTION_EXPORT IsNotNull final : public NullnessPredicate { | ||
| public: | ||
| template <typename T, typename R> | ||
| explicit IsNotNull(R T::* fn) : NullnessPredicate(fn, "IS NOT NULL") {} | ||
| }; | ||
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| /// A wrapper for a comparison predicate, for which the value of the | ||
| /// struct member is required to be greater than a given control value | ||
| class REFLECTION_EXPORT GreaterThan final : public QueryPredicate { | ||
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@@ -189,6 +265,14 @@ class REFLECTION_EXPORT GreaterThan final : public QueryPredicate { | |
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| template <typename T> | ||
| explicit GreaterThan(double T::* fn, double value) : QueryPredicate(fn, value, ">") {} | ||
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| template <typename T> | ||
| explicit GreaterThan(fcpp::optional_t<int64_t> T::* fn, fcpp::optional_t<int64_t> value) | ||
| : QueryPredicate(fn, value, ">") {} | ||
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| template <typename T> | ||
| explicit GreaterThan(fcpp::optional_t<double> T::* fn, fcpp::optional_t<double> value) | ||
| : QueryPredicate(fn, value, ">") {} | ||
| }; | ||
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| /// A wrapper for a comparison predicate, for which the value of the | ||
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@@ -203,6 +287,14 @@ class REFLECTION_EXPORT GreaterThanOrEqual final : public QueryPredicate { | |
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| template <typename T> | ||
| explicit GreaterThanOrEqual(double T::* fn, double value) : QueryPredicate(fn, value, ">=") {} | ||
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| template <typename T> | ||
| explicit GreaterThanOrEqual(fcpp::optional_t<int64_t> T::* fn, fcpp::optional_t<int64_t> value) | ||
| : QueryPredicate(fn, value, ">=") {} | ||
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| template <typename T> | ||
| explicit GreaterThanOrEqual(fcpp::optional_t<double> T::* fn, fcpp::optional_t<double> value) | ||
| : QueryPredicate(fn, value, ">=") {} | ||
| }; | ||
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| /// A wrapper for a comparison predicate, for which the value of the | ||
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@@ -217,6 +309,14 @@ class REFLECTION_EXPORT SmallerThan final : public QueryPredicate { | |
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| template <typename T> | ||
| explicit SmallerThan(double T::* fn, double value) : QueryPredicate(fn, value, "<") {} | ||
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| template <typename T> | ||
| explicit SmallerThan(fcpp::optional_t<int64_t> T::* fn, fcpp::optional_t<int64_t> value) | ||
| : QueryPredicate(fn, value, "<") {} | ||
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| template <typename T> | ||
| explicit SmallerThan(fcpp::optional_t<double> T::* fn, fcpp::optional_t<double> value) | ||
| : QueryPredicate(fn, value, "<") {} | ||
| }; | ||
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| /// A wrapper for a comparison predicate, for which the value of the | ||
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@@ -231,6 +331,14 @@ class REFLECTION_EXPORT SmallerThanOrEqual final : public QueryPredicate { | |
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| template <typename T> | ||
| explicit SmallerThanOrEqual(double T::* fn, double value) : QueryPredicate(fn, value, "<=") {} | ||
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| template <typename T> | ||
| explicit SmallerThanOrEqual(fcpp::optional_t<int64_t> T::* fn, fcpp::optional_t<int64_t> value) | ||
| : QueryPredicate(fn, value, "<=") {} | ||
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| template <typename T> | ||
| explicit SmallerThanOrEqual(fcpp::optional_t<double> T::* fn, fcpp::optional_t<double> value) | ||
| : QueryPredicate(fn, value, "<=") {} | ||
| }; | ||
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| /// A wrapper of a compound predicate, which combines two other predicates, | ||
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This line relies on FetchContent's
SOURCE_SUBDIRhandling to avoid adding functional_cpp's own CMake project, but I checkedcmake --help-module FetchContentand that support is markedversionadded 3.18while this project still advertisescmake_minimum_required(VERSION 3.14). On CMake 3.14-3.17, configuring this commit won't honor the subdir avoidance and can add functional_cpp's top-levelCMakeLists.txt, pulling its src/tests into this build rather than just the headers; either raise the minimum to 3.18 or fetch the headers withoutSOURCE_SUBDIR.Useful? React with 👍 / 👎.
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Good catch —
SOURCE_SUBDIRinFetchContent_Declareis indeed 3.18+, while this project declares a 3.14 minimum. Fixed in 3ee9551 without raising the minimum: the population is now version-guarded. On CMake < 3.18 we useFetchContent_GetProperties+FetchContent_Populate, which downloads the sources without ever callingadd_subdirectory, so functional_cpp's own src/tests targets stay out of the build; on 3.18+ the originalSOURCE_SUBDIR include+FetchContent_MakeAvailablepath is kept. (FetchContent_Populateis deprecated in CMake 3.30, but that branch is unreachable there since it's behind theVERSION_LESS 3.18check.) Verified with a fresh configure + full build + 83/83 tests passing.Generated by Claude Code