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ParseException with Expressions containing Convert method #401

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kyleherzog opened this issue Jul 17, 2020 · 3 comments
Open

ParseException with Expressions containing Convert method #401

kyleherzog opened this issue Jul 17, 2020 · 3 comments
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@JonathanMagnan

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@kyleherzog
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@kyleherzog kyleherzog commented Jul 17, 2020

I'm trying to take expressions created on a client, convert them to string by calling ToString, pass the string values to a web endpoint, and then convert them back to expression objects using DynamicExpressionParser.ParseLambda. In most cases this works. However, if i have an expression that results in a Convert method being called, I get the following exception.

System.Linq.Dynamic.Core.Exceptions.ParseException: '.' or '(' or string literal expected

The following simplified test case exhibits the issue.

Expression<Func<byte, bool>> originalExpression = x => x == 1;
var expressionText = originalExpression.ToString();
Console.WriteLine(expressionText);
// Output: x => (Convert(x, Int32) == 1)
var expression = DynamicExpressionParser.ParseLambda<long, bool>(new ParsingConfig(), false, expressionText);
@JonathanMagnan JonathanMagnan self-assigned this Jul 20, 2020
@JonathanMagnan
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@JonathanMagnan JonathanMagnan commented Jul 20, 2020

Hello @kyleherzog ,

Thank you for reporting, we will look at it.

Best Regards,

Jon

Performance Libraries
context.BulkInsert(list, options => options.BatchSize = 1000);
Entity Framework Extensions • Entity Framework Classic • Bulk Operations • Dapper Plus

Runtime Evaluation
Eval.Execute("x + y", new {x = 1, y = 2}); // return 3
C# Eval Function • SQL Eval Function
@JonathanMagnan
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@JonathanMagnan JonathanMagnan commented Jul 20, 2020

Hello @kyleherzog ,

We checked at your issue and I don't think we will support your scenario for now.

What you are currently providing is not an expression, but a string representation which is not exactly a lambda expression.

For example, the following lambda expression working:

var lambdaExpression = "x => Convert.ToInt32(x) == 1";
var expression = DynamicExpressionParser.ParseLambda<long, bool>(new ParsingConfig(), false, lambdaExpression);
var r1 = expression.Compile()(1);

But in your case, the expression string shows the following convert as Convert(x, Int32) which is not valid.

Let me know if that explains correctly why that's currently not working.

Best Regards,

Jon
@StefH
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@StefH StefH commented Jul 23, 2020

@kyleherzog
Maybe this library https://github.com/esskar/Serialize.Linq can help you when you want to serialize / deserialize linq.
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@StefH @kyleherzog @JonathanMagnan
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