How to set value for a key in appsettings.json file during build time

Question

For my ASP.NET core solution, I have an appsettings.json file and it looks like this

{
  "Branch": {
    "Name": "test"
  },
}

If I want to replace value for "Branch.Name" to some other text, for example "prod" at build time. How do I achieve that?

EDIT: I am aware of the "ASPNETCORE_ENVIRONMENT" environment variable and environment-specific appsettings file for .net core. But unfortunately, for some reason hard to explain, I still need to set value for a key in "appsettings.json" file at build time...

What does "build time" mean? Some services (e.g. DevOps and Octopus Deploy) support JSON substitution... — Kirk Larkin
– Kirk Larkin, Commented Sep 17, 2019 at 21:12
@KirkLarkin, I use bitbucket pipeline. Does it support JSON substitution ? — sean717
– sean717, Commented Sep 17, 2019 at 21:16

Chris Pratt · Accepted Answer · 2019-09-17 20:34:35Z

2

This is not how configuration works in ASP.NET Core. It works on an override system, so instead of literally changing values, you override those values with a more prominent source.

By default, appsettings.json is actually the least priority config source. It can be overridden by all of environment-specific JSON (appsettings.Production.json for example), environment variables, and/or command-line arguments.

For the purposes here, you should be looking at environment-specific JSON and/or environment variables. For example, if you create an appsettings.Production.json with contents:

{
  "Branch": {
    "Name": "prod"
  },
}

And then set your deployment environment to Production (i.e. ASPNETCORE_ENVIRONMENT environment variable), then Branch.Name will be prod in that environment. Similarly, you can set a Branch:Name environment variable to prod, and this will also override the value.

answered Sep 17, 2019 at 20:34

Chris Pratt

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2 Comments

sean717 Over a year ago

Sorry I forgot to mention that I am aware of the "ASPNETCORE_ENVIRONMENT" environment variable and environment-specific appsettings file for .net core. But unfortunately, for some reason hard to explain, I still need to set value for a key in "appsettings.json" file at build time...

Chris Pratt Over a year ago

There is no mechanism for that. Therefore, it's probably a better idea to focus on the problem of why you think you have to, because there shouldn't be a need.

sean717 · Accepted Answer · 2019-09-25 23:26:03Z

1

Yes, there is no built-in way to do this. I end up solving this by using jq. Read the answer of this question.

answered Sep 25, 2019 at 23:26

sean717

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1 Comment

sean717 Over a year ago

also, I found SlowCheetah can be used for this.

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