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DialectImpl

polyglot_sql::dialects

Trait DialectImpl 

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pub trait DialectImpl {
    // Required method
    fn dialect_type(&self) -> DialectType;

    // Provided methods
    fn tokenizer_config(&self) -> TokenizerConfig { ... }
    fn generator_config(&self) -> GeneratorConfig { ... }
    fn generator_config_for_expr(&self, _expr: &Expression) -> GeneratorConfig { ... }
    fn transform_expr(&self, expr: Expression) -> Result<Expression> { ... }
    fn preprocess(&self, expr: Expression) -> Result<Expression> { ... }
}
Expand description

Trait that each concrete SQL dialect must implement.

DialectImpl provides the configuration hooks and per-expression transform logic that distinguish one dialect from another. Implementors supply:

  • A DialectType identifier.
  • Optional overrides for tokenizer and generator configuration (defaults to generic SQL).
  • An expression-level transform function (transform_expr) that rewrites individual AST nodes for this dialect (e.g., converting NVL to COALESCE).
  • An optional preprocessing step (preprocess) for whole-tree rewrites that must run before the recursive per-node transform (e.g., eliminating QUALIFY).

The default implementations are no-ops, so a minimal dialect only needs to provide dialect_type and override the methods that differ from standard SQL.

Required Methods§

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fn dialect_type(&self) -> DialectType

Returns the DialectType that identifies this dialect.

Provided Methods§

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fn tokenizer_config(&self) -> TokenizerConfig

Returns the tokenizer configuration for this dialect.

Override to customize identifier quoting characters, string escape rules, comment styles, and other lexing behavior.

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fn generator_config(&self) -> GeneratorConfig

Returns the generator configuration for this dialect.

Override to customize identifier quoting style, function name casing, keyword casing, and other SQL generation behavior.

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fn generator_config_for_expr(&self, _expr: &Expression) -> GeneratorConfig

Returns a generator configuration tailored to a specific expression.

Override this for hybrid dialects like Athena that route to different SQL engines based on expression type (e.g., Hive-style generation for DDL, Trino-style for DML). The default delegates to generator_config.

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fn transform_expr(&self, expr: Expression) -> Result<Expression>

Transforms a single expression node for this dialect, without recursing into children.

This is the per-node rewrite hook invoked by transform_recursive. Return the expression unchanged if no dialect-specific rewrite is needed. Transformations typically include function renaming, operator substitution, and type mapping.

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fn preprocess(&self, expr: Expression) -> Result<Expression>

Applies whole-tree preprocessing transforms before the recursive per-node pass.

Override this to apply structural rewrites that must see the entire tree at once, such as eliminate_qualify, eliminate_distinct_on, ensure_bools, or explode_projection_to_unnest. The default is a no-op pass-through.

Implementors§