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rulego-team
118 lines
4.1 KiB
Go
118 lines
4.1 KiB
Go
/*
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* Copyright 2025 The RuleGo Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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Package expr provides expression parsing and evaluation capabilities for StreamSQL.
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This package implements a comprehensive expression engine that supports mathematical operations,
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logical comparisons, function calls, field references, and complex CASE expressions.
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It serves as the foundation for WHERE clauses, HAVING clauses, and computed fields in SQL queries.
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# Core Features
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• Mathematical Operations - Supports arithmetic operators (+, -, *, /, %, ^) with proper precedence
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• Logical Operations - Boolean logic with AND, OR operators and comparison operators (=, !=, <, >, <=, >=, LIKE)
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• Function Integration - Seamless integration with the functions package for built-in and custom functions
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• Field References - Dynamic field access with dot notation support for nested data structures
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• CASE Expressions - Full support for both simple and searched CASE expressions
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• Type Safety - Automatic type conversion and validation during expression evaluation
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• Fallback Support - Integration with expr-lang/expr library for complex expressions
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# Expression Types
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The package supports various expression node types:
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// Basic types
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TypeNumber - Numeric constants (integers and floats)
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TypeString - String literals with proper escaping
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TypeField - Field references (e.g., "temperature", "device.id")
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TypeOperator - Binary and unary operators
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TypeFunction - Function calls with argument validation
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TypeParenthesis - Grouped expressions for precedence control
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TypeCase - CASE expressions for conditional logic
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# Usage Examples
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Basic mathematical expression:
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expr, err := NewExpression("temperature * 1.8 + 32")
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if err != nil {
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log.Fatal(err)
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}
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result, err := expr.Evaluate(data)
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Logical expression with field references:
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expr, err := NewExpression("temperature > 25 AND humidity < 60")
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result, err := expr.Evaluate(data)
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Function call expression:
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expr, err := NewExpression("UPPER(device_name) LIKE 'SENSOR%'")
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result, err := expr.Evaluate(data)
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CASE expression for conditional logic:
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expr, err := NewExpression(`
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CASE
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WHEN temperature > 30 THEN 'hot'
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WHEN temperature > 20 THEN 'warm'
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ELSE 'cold'
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END
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`)
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result, err := expr.Evaluate(data)
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# Operator Precedence
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The expression parser follows standard mathematical precedence rules:
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1. Parentheses (highest)
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2. Power (^)
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3. Multiplication, Division, Modulo (*, /, %)
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4. Addition, Subtraction (+, -)
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5. Comparison (>, <, >=, <=, LIKE, IS)
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6. Equality (=, ==, !=, <>)
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7. Logical AND
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8. Logical OR (lowest)
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# Error Handling
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The package provides comprehensive error handling with detailed error messages:
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• Syntax validation during expression creation
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• Type checking during evaluation
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• Function argument validation
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• Graceful fallback to expr-lang for unsupported expressions
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# Performance Considerations
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• Expressions are parsed once and can be evaluated multiple times
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• Built-in operator optimization for common mathematical operations
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• Lazy evaluation for logical operators (short-circuiting)
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• Efficient field access caching for repeated evaluations
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• Automatic fallback to optimized expr-lang library when needed
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# Integration
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This package integrates seamlessly with other StreamSQL components:
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• Functions package - For built-in and custom function execution
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• Types package - For data type definitions and conversions
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• Stream package - For real-time expression evaluation in data streams
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• RSQL package - For SQL parsing and expression extraction
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*/
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package expr
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