Today I learned the ASPNET Core reads appsettings into a key-value pair dictionary. This is outlined in the Hierarchical configuration data section of the Configuration documentation:
The Configuration API is capable of maintaining hierarchical configuration data by flattening the hierarchical data with the use of a delimiter in the configuration keys.
This can be problematic if this isn’t known. For instance consider an array in your appsettings.json:
{
"myproperty": {
"myarray": [
{
"name": "one"
},
{
"name": "two"
}
]
}
}
This would flatten into:
"myproperty:myarray:0:name" = "one"
"myproperty:myarray:1:name" = "two"
The problem occurs when you go to override the array in another environment appsettings.production.json:
{
"myproperty": {
"myarray": [
{
"name": "override all elements of the myarray"
}
]
}
}
Before knowing this I would have expected one element of myarray containing the value “override all elements of the myarray”. I now know this wouldn’t be the case, and that it would actually would be:
"myproperty:myarray:0:name" = "override all elements of the myarray"
"myproperty:myarray:1:name" = "two"
That extra appsetting value might be fine, or it might be a dragon - hence this blog post.
The learning for me is to only put values into appsettings.json that you want to have in each environment. For me I’ll now use appsettings.local.json as a local environment.
Hope this helps you out!