MySQL Overview

Weasel.MySql provides schema management and migration support for MySQL databases using the MySqlConnector driver.

Installation

dotnet add package Weasel.MySql

Key Components

• MySqlProvider -- Singleton at MySqlProvider.Instance that handles type mappings and identifier parsing. The default schema is public; see Schemas are databases.
• MySqlMigrator -- Generates DDL scripts and executes schema migrations. Identifiers are quoted with backticks.

Supported Schema Objects

Object	Class	Namespace
Tables	Table	Weasel.MySql.Tables
Sequences	Sequence	Weasel.MySql

Connection String

Weasel.MySql uses standard MySQL connection strings compatible with MySqlConnector:

var connectionString = "Server=localhost;Database=mydb;User=root;Password=YourPassword;";

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Type Mappings

.NET Type	MySQL Type
string	VARCHAR(255)
int	INT
long	BIGINT
bool	TINYINT(1)
decimal	DECIMAL(18,2)
double	DOUBLE
DateTime	DATETIME
Guid	CHAR(36)
byte[]	BLOB

Creating a Migrator

var migrator = new MySqlMigrator();

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The migrator can ensure the target database exists:

await using var conn = new MySqlConnection(connectionString);
await migrator.EnsureDatabaseExistsAsync(conn);
// Generates: CREATE DATABASE IF NOT EXISTS `mydb`;

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Schemas are databases

MySQL has no schemas inside a database: CREATE SCHEMA is a synonym for CREATE DATABASE. So a Weasel schema name is a MySQL database name, and mydb.users is the table users in the database mydb.

You write	DDL targets	Introspection reads
new Table("mydb.users")	`mydb`.`users`	TABLE_SCHEMA = 'mydb'
new Table("users")	`public`.`users`	TABLE_SCHEMA = 'public'

A table with no schema is not placed in the connection's database. It is placed in a database named public, and the migration fails with 1142 CREATE command denied or 1049 Unknown database 'public' unless that database exists. Name the database explicitly -- the connection's own, if that is where the table belongs:

var database = new MySqlConnectionStringBuilder(connectionString).Database;
var table = new Table(new MySqlObjectName(database, "users"));

A migration creates each database it mentions that does not exist yet (CREATE DATABASE IF NOT EXISTS), which needs the CREATE privilege on it. A database that already exists -- the connection's own, typically -- is not created again, so a user that may alter the tables of a database but not create databases can still apply a delta that only changes existing tables.

Identifiers

MySQL delimits with backticks and delimits unconditionally — it is the one provider for which "was this name left bare?" is never the right question. An embedded backtick is escaped by doubling it. A backslash is rejected outright: it is an escape character inside MySQL string literals unless NO_BACKSLASH_ESCAPES is set, so a trailing one would swallow the closing quote of a literal a name is written into.

9.25 normalizes identifiers on the way into the model, which is visible in two places:

• Table(DbObjectName) normalizes to MySqlObjectName, so Table.Identifier.QualifiedName renders as `schema`.`name` rather than schema.name. Table(string) already parsed through MySqlProvider and is unaffected.
• table.Identifier no longer compares equal to a plain new DbObjectName(schema, name) for the same table. That inequality was the fix, not the bug — a hand-built identifier never matched the catalog, so foreign keys reported drift on every check.

See Identifiers and Quoting for the cross-provider rules and Upgrading to 9.25 for the migration notes.