mirror of
https://github.com/getml/sqlgen.git
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Dr. Patrick Urbanke (劉自成)
113 lines
2.4 KiB
Markdown
113 lines
2.4 KiB
Markdown
# Defining tables
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`sqlgen` provides a type-safe way to define database tables using C++ structs. It automatically handles table creation, schema management, and nullability through C++ types.
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## Usage
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### Basic Table Definition
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Define a table using a simple C++ struct:
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```cpp
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struct People {
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std::string first_name;
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std::string last_name;
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uint age;
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};
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```
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When you write data to this table, it will be automatically created if it doesn't exist:
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```cpp
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const auto people = std::vector<People>(...);
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const auto result = sqlgen::write(conn, people);
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```
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This generates SQL similar to:
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```sql
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CREATE TABLE IF NOT EXISTS "People"(
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"first_name" TEXT NOT NULL,
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"last_name" TEXT NOT NULL,
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"age" INTEGER NOT NULL
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);
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```
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### Custom Table Names
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Override the default table name using a static member:
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```cpp
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struct People {
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constexpr static const char* tablename = "PEOPLE";
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std::string first_name;
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std::string last_name;
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uint age;
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};
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```
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This generates SQL with the custom table name:
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```sql
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CREATE TABLE IF NOT EXISTS "PEOPLE"(
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"first_name" TEXT NOT NULL,
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"last_name" TEXT NOT NULL,
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"age" INTEGER NOT NULL
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);
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```
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### Custom Schemas
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Define a table within a specific schema:
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```cpp
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struct People {
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constexpr static const char* schema = "my_schema";
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std::string first_name;
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std::string last_name;
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uint age;
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};
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```
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This generates SQL with the schema specification:
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```sql
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CREATE TABLE IF NOT EXISTS "my_schema"."People"(
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"first_name" TEXT NOT NULL,
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"last_name" TEXT NOT NULL,
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"age" INTEGER NOT NULL
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);
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```
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### Nullable Fields
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As we have seen, all columns are non-nullable by default. But what if we do want
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nullability?
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As with reflect-cpp, `std::optional`, `std::shared_ptr` and `std::unique_ptr` are interpreted as nullable types,
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but it is strongly recommended that you use `std::optional`.
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So you can create nullable fields as follows:
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```cpp
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struct People {
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rfl::PrimaryKey<std::string> first_name;
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std::string last_name;
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std::optional<uint> age;
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};
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```
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## Notes
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- All fields are non-nullable by default
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- Nullable fields can be defined using:
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- `std::optional<T>` (strongly recommended)
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- `std::shared_ptr<T>`
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- `std::unique_ptr<T>`
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- Use `std::nullopt` or `nullptr` to represent NULL values
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- The exact SQL generated may vary between database dialects
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- Table names are inferred from struct names by default
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- Custom table names and schemas can be specified using static members
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