How to escape a backslash in a string while decoding it in a JSON object

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1

Hello

Let me define the problem first.

I have a jsonb database column called results in my Postgres DB. When I save a value (i.e 12\25) it saves like that in the DB.

{"attri": {"input": "12\\25"}}

Now I have a JSON string

"{ "custom_key": "@attri.input"}"

When I replace the above map values in this string I got the following results.

"{\"custom_key\": \"12\\25\"}"

All this is good and working as expected but when I try to decode this string into JSON

Like this Jason.decode("{\"custom_key\": \"12\\25\"}") it gives me an error.

I also try to escape the value before replacing it in string and in that case, it gives me the following results.

"{ \"custom_key\": \"\"12\\\\25\"\"}"

And I am not able to parse this string into JSON as well.

Please let me know in case I am missing something here or you need any other clarification on the problem.

2

Forum tip: telling the reader “it gives me an error” is vastly less helpful than showing the reader the output of trying that:

iex(1)> Jason.decode("{\"custom_key\": \"12\\25\"}")
{:error,
 %Jason.DecodeError{
   data: "{\"custom_key\": \"12\\25\"}",
   position: 19,
   token: nil
 }}

Printing the string involved makes it clearer what’s going on:

iex(2)> s = "{\"custom_key\": \"12\\25\"}"          
"{\"custom_key\": \"12\\25\"}"
iex(3)> IO.puts s
{"custom_key": "12\25"}
:ok

So the JSON parser complains about the lone \ in the input.

In your second example, this happens:

iex(4)> s = "{ \"custom_key\": \"\"12\\\\25\"\"}"
"{ \"custom_key\": \"\"12\\\\25\"\"}"
iex(5)> Jason.decode(s)
{:error,
 %Jason.DecodeError{
   data: "{ \"custom_key\": \"\"12\\\\25\"\"}",
   position: 18,
   token: nil
 }}
iex(6)> IO.puts s
{ "custom_key": ""12\\25""}
:ok

Now the extra "s around 12\\25 throw the whole thing off.

My advice: don’t try to replace values in JSON by string-replacing the whole thing - parse the JSON, do the replacements there, then re-encode.

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