Class: SqlGenius::Core::QueryExplainer

Inherits:
Object
  • Object
show all
Defined in:
lib/sql_genius/core/query_explainer.rb

Overview

Runs EXPLAIN against a SELECT query via a Core::Connection. Optionally skips SQL validation (used for explaining captured slow queries from mysql’s own logs where the exact text may include references to otherwise-blocked tables).

Rejects obviously-truncated SQL — captured slow queries from the slow query log are capped at ~2000 characters, so if the last character doesn’t look like a valid terminator we refuse to try. This avoids confusing EXPLAIN errors from partial statements.

Reuses Core::QueryRunner::Rejected for validation failures so callers can rescue one error type for both runners.

Defined Under Namespace

Classes: Truncated

Instance Method Summary collapse

Constructor Details

#initialize(connection, config) ⇒ QueryExplainer

Returns a new instance of QueryExplainer.



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# File 'lib/sql_genius/core/query_explainer.rb', line 20

def initialize(connection, config)
  @connection = connection
  @config = config
end

Instance Method Details

#explain(sql, skip_validation: false) ⇒ Object 



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# File 'lib/sql_genius/core/query_explainer.rb', line 25

def explain(sql, skip_validation: false)
  unless skip_validation
    error = SqlValidator.validate(
      sql,
      blocked_tables: @config.blocked_tables,
      connection: @connection,
    )
    raise QueryRunner::Rejected, error if error
  end

  clean_sql = normalize_placeholders(SqlValidator.normalize_identifier_quotes(sql, @connection).gsub(/;\s*\z/, ""))

  unless looks_complete?(clean_sql)
    raise Truncated, "This query appears to be truncated and cannot be explained."
  end

  @connection.exec_query("EXPLAIN #{clean_sql}")
end