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@crallen
Created February 26, 2014 20:46
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Json.NET contract resolver that uses Ruby-style lowercase with underscore naming conventions.
using Newtonsoft.Json.Serialization;
namespace ConsoleApplication3
{
public class SnakeCaseContractResolver : DefaultContractResolver
{
protected override string ResolvePropertyName(string propertyName)
{
return GetSnakeCase(propertyName);
}
private string GetSnakeCase(string input)
{
if (string.IsNullOrEmpty(input))
return input;
var buffer = "";
for (var i = 0; i < input.Length; i++)
{
var isLast = (i == input.Length - 1);
var isSecondFromLast = (i == input.Length - 2);
var curr = input[i];
var next = !isLast ? input[i + 1] : '\0';
var afterNext = !isSecondFromLast && !isLast ? input[i + 2] : '\0';
buffer += char.ToLower(curr);
if (!char.IsDigit(curr) && char.IsUpper(next))
{
if (char.IsUpper(curr))
{
if (!isLast && !isSecondFromLast && !char.IsUpper(afterNext))
buffer += "_";
}
else
buffer += "_";
}
if (!char.IsDigit(curr) && char.IsDigit(next))
buffer += "_";
if (char.IsDigit(curr) && !char.IsDigit(next) && !isLast)
buffer += "_";
}
return buffer;
}
}
}
@Timovzl
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Timovzl commented Apr 11, 2016

// (Preceded by a lowercase character or digit) (a capital) => The character prefixed with an underscore
var result = Regex.Replace(input, "(?<=[a-z0-9])[A-Z]", m => "_" + m.Value);
result = result.ToLowerInvariant();
  • This works for both PascalCase and camelCase.
  • It creates no leading or trailing underscores.
  • It leaves in tact any sequences of non-word characters and underscores in the string, because they would seem intentional, e.g. __HiThere_Guys becomes __hi_there_guys.
  • Digit suffixes are (intentionally) considered part of the word, e.g. NewVersion3 becomes new_version3.
  • Digit prefixes follow the original casing, e.g. 3VersionsHere becomes 3_versions_here, but 3rdVersion becomes 3rd_version.

@jorgeyanesdiez
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I agree, I was using Regex.Replace(input, @"([a-z0-9])([A-Z])", "$1_$2").ToLowerInvariant();
I think the ?<= in the regex adds unnecessary complexity, am I wrong?

@Timovzl
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Timovzl commented Jun 9, 2016

Interesting idea. I'm not sure how the ?<= (lookbehind) is handled by the regex engine. It's that vs. replacing more data, which at least is guaranteed to be linear time. And yours looks simpler too, so agreed.

@Lechus
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Lechus commented Jun 28, 2017

Works! Thanks.

@snboisen
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snboisen commented Aug 8, 2017

Nowadays you don't need a custom contract resolver, just do:

var settings = new JsonSerializerSettings
{
    ContractResolver = new DefaultContractResolver
    {
        NamingStrategy = new SnakeCaseNamingStrategy()
    }
};

@Andrei-Fogoros
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Hi Chris,
Thank you for your code! :)

Can you please tell me what is the license for the above code?

Regards,
Andrei

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