In the process of project development , You just need to use the processing scenario of evaluating string expressions , So I looked for several qualified third-party components LambdaParser、DynamicExpresso、Z.Expressions, They have different functions , But they can basically meet the requirements . Both of them can evaluate string expressions according to related parameters , This essay introduces the use code of the three , And sum up some of the experience .
Evaluation of mathematical expressions should be the most common , Generally, if we need to calculate in the application , It is necessary to type the parameter , And then perform corresponding calculation in the background . But if you are calculating some formulas or formulas that match , Especially when the parameters are not certain , This is more troublesome . Leverage third-party components , Quick evaluation of expressions , It can meet many of our actual project needs , And it's easy to handle .
These third-party components , Their GitHub Or official website address ：
https://github.com/nreco/lambdaparser
https://github.com/dynamicexpresso/DynamicExpresso
https://eval-expression.net/eval-execute
however Z.Expressions Is the charge , The first two are free .
The scenario where I use string expressions to evaluate , The main idea is to SQL Conditional expression , Convert to a normal string expression , Then according to the parameter value of the object , Perform evaluation processing , These expression evaluation components support such operations , In order to better demonstrate their use effect and code , We created a case code to test and verify , Confirm to meet my actual needs .
1、Z.Expressions.Eval Expression parsing
Z.Expression.Eval It's a free and open source （ Follow up charges ）, Extensible , Ultra lightweight formulaic language parsing and execution toolkit , Can be resolved at run time C# An open source free component of expressions .Z.Expressions from 2.0 Started to support NetCore, But for a fee . Reference address ：https://riptutorial.com/eval-expression/learn/100000/getting-started perhaps https://eval-expression.net/eval-execute.
Parse at run time C# expression , For example, some salary or cost accounting systems , You need to dynamically configure the calculation expression in the background , So as to calculate and evaluate .
The following describes several different case codes and verifies the output results
Anonymous type handling
// Anonymous types
string expression = "a*2 + b*3 - 3";
int result = Eval.Execute<int>(expression, new { a = 10, b = 5 });
Console.WriteLine("{0} = {1}", expression, result); //a*2 + b*3 - 3 = 32
Specify the parameters
// Specify the parameters
expression = "{0}*2 + {1}*3 - 3";
result = Eval.Execute<int>(expression, 10, 5);
Console.WriteLine("{0} = {1}", expression, result);//{0}*2 + {1}*3 - 3 = 32
Class object
// Class object
expression = "a*2 + b*3 - 3";
dynamic expandoObject = new ExpandoObject();
expandoObject.a = 10;
expandoObject.b = 5; result = Eval.Execute<int>(expression, expandoObject);
Console.WriteLine("{0} = {1}", expression, result); //a*2 + b*3 - 3 = 32
A dictionary object
// A dictionary object
expression = "a*2 + b*3 - 3";
var values = new Dictionary<string, object>()
{
{ "a", 10 },
{ "b", 5 }
}; result = Eval.Execute<int>(expression, values);
Console.WriteLine("{0} = {1}", expression, result);//a*2 + b*3 - 3 = 32
Delegate type
// Delegate type 1
expression = "{0}*2 + {1}*3";
var compiled = Eval.Compile<Func<int, int, int>>(expression);
result = compiled(10, 15);
Console.WriteLine("{0} = {1}", expression, result);//{0}*2 + {1}*3 = 65 // Delegate type 2
expression = "a*2 + b*3";
compiled = Eval.Compile<Func<int, int, int>>(expression, "a", "b");
result = compiled(10, 15);
Console.WriteLine("{0} = {1}", expression, result);//a*2 + b*3 = 65
String extension support
// String extension support - Anonymous types
expression = "a*2 + b*3 - 3";
result = expression.Execute<int>(new { a = 10, b = 5 });
Console.WriteLine("{0} = {1}", expression, result);//a*2 + b*3 - 3 = 32 // String extension support - Dictionary type
expression = "a*2 + b*3 - 3";
values = new Dictionary<string, object>()
{
{ "a", 10 },
{ "b", 5 }
};
result = expression.Execute<int>(values);
Console.WriteLine("{0} = {1}", expression, result);//a*2 + b*3 - 3 = 32
It can be seen that , This component provides very rich expression operation and evaluation processing methods .
2、NReco.LambdaParser Expression parsing
I like the handling of this component , The main reason is that it can pass in the dictionary type , In this way, I can easily pass in various types of parameters , And this component is close to SQL grammar , You can set up to use the regular = Instead of expression ==, So for SQL Statement is convenient .
Its case code is as follows .
/// <summary>
/// NReco.LambdaParser Expression parsing
/// </summary>
private void btnLamdaParser_Click(object sender, EventArgs e)
{
var lambdaParser = new NReco.Linq.LambdaParser(); var dict = new Dictionary<string, object>();
dict["pi"] = 3.14M;
dict["one"] = 1M;
dict["two"] = 2M;
dict["test"] = "test";
Console.WriteLine(lambdaParser.Eval("pi>one && 0<one ? (1+8)/3+1*two : 0", dict)); // --> 5
Console.WriteLine(lambdaParser.Eval("test.ToUpper()", dict)); // --> TEST Console.WriteLine(lambdaParser.Eval("pi>one && 0<one ", dict)); // --> True
Console.WriteLine(lambdaParser.Eval("test.ToUpper()", dict)); // --> TEST
}
It also supports arithmetic symbol operations such as ：+, -, *, /, %, And conventional logical judgment ：==, !=, >, <, >=, <=, If necessary, it allows you to = As == Compare , Then set the properties AllowSingleEqualSign = true that will do , The following code .
var lambdaParser = new LambdaParser();
lambdaParser.AllowSingleEqualSign = true;// have access to = As a logical judgment , Such as Title ="Leader", without Title =="Leader"
var evalResult = lambdaParser.Eval(repalce, dict);
This component does not provide too many examples , But its examples provide key points , Basically, it can meet our actual expression evaluation processing requirements .
3、DynamicExpresso Expression parsing
be relative to LambdaParser The concise 、Z.Expressions Charge processing ,Dynamic Expresso It can be said to provide a very powerful 、 Free and open source processing class library , It provides many ways to implement expression evaluation .
A simple string expression evaluates to the following code
var interpreter = new Interpreter();
var result = interpreter.Eval("8 / 2 + 2");
But generally, we need to pass in certain parameters for expression evaluation .
var target = new Interpreter();
double result = target.Eval<double>("Math.Pow(x, y) + 5",
new Parameter("x", typeof(double), 10),
new Parameter("y", typeof(double), 2));
perhaps
var interpreter = new Interpreter();
var parameters = new[] {
new Parameter("x", 23),
new Parameter("y", 7)
};
Assert.AreEqual(30, interpreter.Eval("x + y", parameters));
Or assign a specified parameter
var target = new Interpreter().SetVariable("myVar", 23);
Assert.AreEqual(23, target.Eval("myVar"));Dealing with dictionary types , It's the way I like , Its case code is as follows .
var interpreter = new Interpreter();
var dict = new Dictionary<string, object>();
dict.Add("a", 1.0);
dict.Add("b", 2);
dict.Add("d", 4);
dict.Add("e", 5);
dict.Add("str", 'f'); foreach (var v in dict)
{
object value = v.Value;
int para = 0;
if (int.TryParse(v.Value.ToString(), out para))
{
value = (float)para;
}
interpreter.SetVariable(v.Key, value);
}
Console.WriteLine(interpreter.Eval("a+b").ToString()); //3
Console.WriteLine(interpreter.Eval("a/b").ToString()); //0.5
Console.WriteLine(interpreter.Eval("a > b").ToString()); //False
Console.WriteLine(interpreter.Eval("str == 'f'").ToString()); //True
For class attribute expression query , The test code is as follows
var customers = new List<Customer> {
new Customer() { Name = "David", Age = 31, Gender = 'M' },
new Customer() { Name = "Mary", Age = 29, Gender = 'F' },
new Customer() { Name = "Jack", Age = 2, Gender = 'M' },
new Customer() { Name = "Marta", Age = 1, Gender = 'F' },
new Customer() { Name = "Moses", Age = 120, Gender = 'M' },
};
string whereExpression = "customer.Age > 18 && customer.Gender == 'F'";
Func<Customer, bool> dynamicWhere = interpreter.ParseAsDelegate<Func<Customer, bool>>(whereExpression, "customer");
Console.WriteLine(customers.Where(dynamicWhere).Count());//=> 1
var customer_query = (new List<Customer> {
new Customer() { Name = "David", Age = 31, Gender = 'M' },
new Customer() { Name = "Mary", Age = 29, Gender = 'F' },
new Customer() { Name = "Jack", Age = 2, Gender = 'M' },
new Customer() { Name = "Marta", Age = 1, Gender = 'F' },
new Customer() { Name = "Moses", Age = 120, Gender = 'M' },
}).AsQueryable();
whereExpression = "customer.Age > 18 && customer.Gender == 'F'";
var expression = interpreter.ParseAsExpression<Func<Customer, bool>>(whereExpression, "customer");
Console.WriteLine(customer_query.Where(expression).Count());//=> 14、SQL Regular expression and string evaluation processing of conditional statements
We introduced several components of expression evaluation processing , They can basically meet the actual evaluation processing , Only the functions provided are emphasized .
I mainly want to use it to evaluate Boolean values of specific expressions , Judge whether the expression satisfies the condition .
For example, for sql Conditional statements :(Amount> 500 and Title ='Leader') or Age> 32, And a set of parameters of the dictionary object , I hope to be able to extract the Amount、Title、Leader、Age Such a key , Then assign values to the dictionary , To determine the value of the expression .
because sql Expression and C# The expression logic syntax of the code is different , We need to replace and Or For practical && || character , So given a replacement regular expression ：\sand|\sor
And I need to extract the key value content of the conditional statement first , Then get the specified key parameters , Then you should also provide a regular expression ：\w*[^>=<!'()\s] , This regular expression is mainly used to extract specific character matches .
Extracted content C# The code logic is as follows .
private void btnRegexExtract_Click(object sender, EventArgs e)
{
var source = this.txtSource.Text; // Replace part of the content first \sand|\sor
source = Regex.Replace(source, this.txtReplaceRegex.Text, "");// Replace expression
// Add a line of record main content
this.txtContent.Text += " Replace the contents after regular expression :";
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.Text += source;
this.txtContent.AppendText(Environment.NewLine); // In matching content processing
var regex = new Regex(this.txtRegex.Text);
var matches = regex.Matches(source); // Traversal to get each matching content
var fieldList = new List<string>();
int i = 0;
foreach (Match match in matches)
{
this.txtContent.AppendText(match.Value);
this.txtContent.AppendText(Environment.NewLine);
if (i++ % 2 == 0)
{
fieldList.Add(match.Value);
}
}
this.txtContent.AppendText(" Get the expression Key ：");
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(fieldList.ToJson());
this.txtContent.AppendText(Environment.NewLine); var repalce = ReplaceExpress(this.txtSource.Text);
this.txtContent.AppendText(" Replace And=>&& or=>|| '=> \" After the operator :");
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(repalce);
}
/// <summary>
/// Replace And=>&& or=>|| '=> \" After the operator
/// </summary>
/// <param name="source"></param>
/// <returns></returns>
private string ReplaceExpress(string source)
{
// Operator replacement expression
var repalce = Regex.Replace(source, @"\sand\s", " && "); //and => &&
repalce = Regex.Replace(repalce, @"\sor\s", " || "); //or => ||
repalce = Regex.Replace(repalce, @"'", "\""); //'=> \" return repalce;
}
The result of expression processing is as follows
Its logic code is as follows .
private void btnRunExpression_Click(object sender, EventArgs e)
{
// Operator replacement expression
var repalce = ReplaceExpress(this.txtSource.Text);
this.txtContent.Text = " Replace And=>&& or=>|| '=> \" After the operator :";
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.Text += repalce;
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(Environment.NewLine); //(Amount> 500 and Title ='Leader') or Age> 32
var dict = new Dictionary<string, object>();
dict["Amount"] = 600;
dict["Title"] = "Leader";
dict["Age"] = 40; this.txtContent.AppendText(" Dictionary content ");
foreach(var key in dict.Keys)
{
this.txtContent.AppendText($"{key}:{dict[key]} ");
}
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(Environment.NewLine); //var valComparer = new ValueComparer() { NullComparison = ValueComparer.NullComparisonMode.Sql };
//var lambdaParser = new LambdaParser(valComparer);
var lambdaParser = new LambdaParser();
lambdaParser.AllowSingleEqualSign = true;// have access to = As a judgment , Such as Title ="Leader", without Title =="Leader"
var express1 = "(Amount> 500 && Title = \"Leader\") or Age>30";
var result1 = lambdaParser.Eval(express1, dict);
this.txtContent.AppendText("LambdaParser Expression processing ：");
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express1 + " => " + result1); var express2 = "( Amount> 500 && Title =\"leader\" )"; // String comparison （''=> ""）
var result2 = lambdaParser.Eval(express2, dict);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express2 + " => " + result2); var express3 = "Amount> 500";
var result3 = lambdaParser.Eval(express3, dict);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express3 + " => " + result3); var express4 = "Title = \"Leader\" "; // String comparison （''=> ""）
var result4 = lambdaParser.Eval(express4, dict);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express4 + " => " + result4); this.txtContent.AppendText(Environment.NewLine);
Console.WriteLine(lambdaParser.Eval("Title.ToString()", dict)); // --> Leader //DynamicExpresso Expression parsing processing
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText("DynamicExpresso Expression parsing processing ："); var interpreter = new Interpreter();
foreach (var v in dict)
{
interpreter.SetVariable(v.Key, v.Value);
}
//express3 = "Amount> 500";
var result33 = interpreter.Eval(express3);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express3 + " => " + result33); // Use '' error , String comparison requires ""
try
{
express4 = "Title == \"Leader\" ";
var result44 = interpreter.Eval(express4);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express4 + " => " + result44);
}
catch(Exception ex)
{
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express4 + ", Parsing error => " + ex.Message);
} //var dict = new Dictionary<string, object>();
//dict["Amount"] = 600;
//dict["Title"] = "Leader";
//dict["Age"] = 40;
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText("Z.Expressions.Eval Expression parsing ：");
var result333 = express3.Execute<bool>(dict);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express3 + " => " + result333); express4 = "Title == 'Leader'"; //Z.Expressions Acceptable ' Instead of "
var result444 = express4.Execute<bool>(dict);
this.txtContent.AppendText(Environment.NewLine);
this.txtContent.AppendText(express4 + " => " + result444);
}
So we can convert SQL The conditional expression is actual C# expression , And assign parameters , Implementation of dynamic expression evaluation processing .
stay C# Third party components are used in development LambdaParser、DynamicExpresso、Z.Expressions, Realize dynamic parsing / More articles on evaluating string expressions
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