refactor: database interaction and error handling (#10762)

This pull request introduces a significant refactoring of the database
interaction layer, focusing on improving explicitness, transactional
control, and error handling. The core change is the removal of the
stateful `QueryExecutor` from repository instances. Instead, it is now
passed as an argument to each method that interacts with the database.

This change makes transaction management more explicit and flexible, as
the same repository instance can be used with a database pool or a
specific transaction without needing to be re-instantiated.

### Key Changes

- **Explicit `QueryExecutor` Passing:**
- All repository methods (`Get`, `List`, `Create`, `Update`, `Delete`,
etc.) in `InstanceRepository`, `OrganizationRepository`,
`UserRepository`, and their sub-repositories now require a
`database.QueryExecutor` (e.g., a `*pgxpool.Pool` or `pgx.Tx`) as the
first argument.
- Repository constructors no longer accept a `QueryExecutor`. For
example, `repository.InstanceRepository(pool)` is now
`repository.InstanceRepository()`.

- **Enhanced Error Handling:**
- A new `database.MissingConditionError` is introduced to enforce
required query conditions, such as ensuring an `instance_id` is always
present in `UPDATE` and `DELETE` operations.
- The database error wrapper in the `postgres` package now correctly
identifies and wraps `pgx.ErrTooManyRows` and similar errors from the
`scany` library into a `database.MultipleRowsFoundError`.

- **Improved Database Conditions:**
- The `database.Condition` interface now includes a
`ContainsColumn(Column) bool` method. This allows for runtime checks to
ensure that critical filters (like `instance_id`) are included in a
query, preventing accidental cross-tenant data modification.
- A new `database.Exists()` condition has been added to support `EXISTS`
subqueries, enabling more complex filtering logic, such as finding an
organization that has a specific domain.

- **Repository and Interface Refactoring:**
- The method for loading related entities (e.g., domains for an
organization) has been changed from a boolean flag (`Domains(true)`) to
a more explicit, chainable method (`LoadDomains()`). This returns a new
repository instance configured to load the sub-resource, promoting
immutability.
- The custom `OrgIdentifierCondition` has been removed in favor of using
the standard `database.Condition` interface, simplifying the API.

- **Code Cleanup and Test Updates:**
  - Unnecessary struct embeddings and metadata have been removed.
- All integration and repository tests have been updated to reflect the
new method signatures, passing the database pool or transaction object
explicitly.
- New tests have been added to cover the new `ExistsDomain`
functionality and other enhancements.

These changes make the data access layer more robust, predictable, and
easier to work with, especially in the context of database transactions.

backend/v3/storage/database/column.go

@@ -3,8 +3,9 @@ package database
 type Columns []Column
 
 // WriteQualified implements [Column].
-func (m Columns) WriteQualified(builder *StatementBuilder) {
-	for i, col := range m {
+// Columns are separated by ", ".
+func (c Columns) WriteQualified(builder *StatementBuilder) {
+	for i, col := range c {
 		if i > 0 {
 			builder.WriteString(", ")
 		}
@@ -13,8 +14,9 @@ func (m Columns) WriteQualified(builder *StatementBuilder) {
 }
 
 // WriteUnqualified implements [Column].
-func (m Columns) WriteUnqualified(builder *StatementBuilder) {
-	for i, col := range m {
+// Columns are separated by ", ".
+func (c Columns) WriteUnqualified(builder *StatementBuilder) {
+	for i, col := range c {
 		if i > 0 {
 			builder.WriteString(", ")
 		}
@@ -22,11 +24,33 @@ func (m Columns) WriteUnqualified(builder *StatementBuilder) {
 	}
 }
 
+// Equals implements [Column].
+func (c Columns) Equals(col Column) bool {
+	if col == nil {
+		return c == nil
+	}
+	other, ok := col.(Columns)
+	if !ok || len(other) != len(c) {
+		return false
+	}
+	for i, col := range c {
+		if !col.Equals(other[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+var _ Column = (Columns)(nil)
+
 // Column represents a column in a database table.
 type Column interface {
-	// Write(builder *StatementBuilder)
+	// WriteQualified writes the column with the table name as prefix.
 	WriteQualified(builder *StatementBuilder)
+	// WriteUnqualified writes the column without the table name as prefix.
 	WriteUnqualified(builder *StatementBuilder)
+	// Equals checks if two columns are equal.
+	Equals(col Column) bool
 }
 
 type column struct {
@@ -35,7 +59,7 @@ type column struct {
 }
 
 func NewColumn(table, name string) Column {
-	return column{table: table, name: name}
+	return &column{table: table, name: name}
 }
 
 // WriteQualified implements [Column].
@@ -51,35 +75,69 @@ func (c column) WriteUnqualified(builder *StatementBuilder) {
 	builder.WriteString(c.name)
 }
 
-var _ Column = (*column)(nil)
+// Equals implements [Column].
+func (c *column) Equals(col Column) bool {
+	if col == nil {
+		return c == nil
+	}
+	toMatch, ok := col.(*column)
+	if !ok {
+		return false
+	}
+	return c.table == toMatch.table && c.name == toMatch.name
+}
 
-// // ignoreCaseColumn represents two database columns, one for the
-// // original value and one for the lower case value.
-// type ignoreCaseColumn interface {
-// 	Column
-// 	WriteIgnoreCase(builder *StatementBuilder)
-// }
+// LowerColumn returns a column that represents LOWER(col).
+func LowerColumn(col Column) Column {
+	return &functionColumn{fn: functionLower, col: col}
+}
 
-// func NewIgnoreCaseColumn(col Column, suffix string) ignoreCaseColumn {
-// 	return ignoreCaseCol{
-// 		column: col,
-// 		suffix: suffix,
-// 	}
-// }
+// SHA256Column returns a column that represents SHA256(col).
+func SHA256Column(col Column) Column {
+	return &functionColumn{fn: functionSHA256, col: col}
+}
 
-// type ignoreCaseCol struct {
-// 	column Column
-// 	suffix string
-// }
+type functionColumn struct {
+	fn  function
+	col Column
+}
 
-// // WriteIgnoreCase implements [ignoreCaseColumn].
-// func (c ignoreCaseCol) WriteIgnoreCase(builder *StatementBuilder) {
-// 	c.column.WriteQualified(builder)
-// 	builder.WriteString(c.suffix)
-// }
+type function string
 
-// // WriteQualified implements [ignoreCaseColumn].
-// func (c ignoreCaseCol) WriteQualified(builder *StatementBuilder) {
-// 	c.column.WriteQualified(builder)
-// 	builder.WriteString(c.suffix)
-// }
+const (
+	_              function = ""
+	functionLower  function = "LOWER"
+	functionSHA256 function = "SHA256"
+)
+
+// WriteQualified implements [Column].
+func (c functionColumn) WriteQualified(builder *StatementBuilder) {
+	builder.Grow(len(c.fn) + 2)
+	builder.WriteString(string(c.fn))
+	builder.WriteRune('(')
+	c.col.WriteQualified(builder)
+	builder.WriteRune(')')
+}
+
+// WriteUnqualified implements [Column].
+func (c functionColumn) WriteUnqualified(builder *StatementBuilder) {
+	builder.Grow(len(c.fn) + 2)
+	builder.WriteString(string(c.fn))
+	builder.WriteRune('(')
+	c.col.WriteUnqualified(builder)
+	builder.WriteRune(')')
+}
+
+// Equals implements [Column].
+func (c *functionColumn) Equals(col Column) bool {
+	if col == nil {
+		return c == nil
+	}
+	toMatch, ok := col.(*functionColumn)
+	if !ok || toMatch.fn != c.fn {
+		return false
+	}
+	return c.col.Equals(toMatch.col)
+}
+
+var _ Column = (*functionColumn)(nil)