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https://github.com/getml/sqlgen.git
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Dr. Patrick Urbanke
99 lines
2.4 KiB
Markdown
99 lines
2.4 KiB
Markdown
# Defining tables
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In sqlgen, tables are defined using C++ structs. In its simplest
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form, this can look like this:
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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 then try to write a vector of `People`,
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the table will be automatically created, if necessary:
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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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In other words, `sqlgen::write(...)` might call the following SQL
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statement under-the-hood:
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```sql
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CREATE TABLE IF NOT EXISTS "People"("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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(As with all SQL examples, the exact code will vary between dialects.)
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## Custom table names
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Obviously, it is very convenient to just infer the table name
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from the name of the struct. But sometimes we don't want that.
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So we can do something like this:
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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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Now, the generated SQL code will look like this:
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```cpp
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CREATE TABLE IF NOT EXISTS "PEOPLE"("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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## Custom schemata
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In a similar manner, you can embed your table in a 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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Now, the generated SQL code will look like this:
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```cpp
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CREATE TABLE IF NOT EXISTS "my_schema"."People"("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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## Nullable types
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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
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as nullable types. 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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You can induce the NULL value by passing `std::nullopt` to age and NULL values
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will be translated to `std::nullopt`.
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