add SettingsBuilder.UseEnvironmentVariable()

Fig.Core/SettingsBuilder.cs

@@ -42,14 +42,32 @@ public SettingsBuilder UseDotEnv(string fileName = ".env", string directory = ".
         /// <remarks>The path separator (default is _) will be translated to a dot</remarks>
         /// </summary>
         /// <param name="prefix">For example FIG_, default is no prefix. </param>
-        /// <param name="dropPrefix">When true, the prefix will not be included in the key</param>
+        /// <param name="dropPrefix">When true, the prefix will not be included in the key. default is true</param>
         /// <returns></returns>
         public SettingsBuilder UseEnvironmentVariables(string prefix = "", bool dropPrefix = true)
         {
             Add(new EnvironmentVariablesSource(prefix, dropPrefix).ToSettingsDictionary());
             return this;
         }
 
+        /// <summary>
+        /// Read a single environment variable
+        /// </summary>
+        /// <param name="name">the name of the environment variable</param>
+        /// <param name="required"></param>
+        /// <returns></returns>
+        /// <exception cref="ConfigurationException">Thrown if the variable is required but not defined</exception>
+        public SettingsBuilder UseEnvironmentVariable(string name, bool required = false)
+        {
+            var val = Environment.GetEnvironmentVariable(name);
+            if (val is null && required) throw new ConfigurationException("Required ENV var not found: " + name);
+            if (val != null) Add(new SettingsDictionary()
+            {
+                [name] = val
+            });
+            return this;
+        }
+
         private void Add(SettingsDictionary settingsDictionary)
         {
             _layeredDictionary.Add(settingsDictionary);

Fig.Tests/ArrayBindingTests.cs

@@ -0,0 +1,30 @@
+using NUnit.Framework;
+
+namespace Fig.Test;
+
+public class ArrayBindingTests
+{
+     [Test]
+     public void CanBindToArray()
+     {
+          var settings = new SettingsBuilder()
+               .UseAppSettingsJson("appsettings.json", required: true)
+               .Build();
+
+          var servers = settings.Get<string[]>("Servers");
+          Assert.AreEqual(2,servers.Length);
+          Assert.AreEqual("10.0.0.1", servers[0]);
+          Assert.AreEqual("10.0.0.2", servers[1]);
+
+          var mySettings = settings.Bind<MySettings>(path:"");
+          Assert.AreEqual(2, mySettings.Servers.Length);
+          Assert.AreEqual("10.0.0.1", mySettings.Servers[0]);
+          Assert.AreEqual("10.0.0.2", mySettings.Servers[1]);
+
+     }
+
+     private class MySettings
+     {
+          public string[] Servers { get; set; }
+     }
+}

Fig.Tests/appsettings.TEST.json

@@ -13,14 +13,5 @@
   "Simpsons" :  [
       { "Name" :  "Bart", "Age" :  12},
       { "Name" :  "Homer", "Age" :  35}
-  ],
-
-  "EnvQualified:PROD" : {
-    "a" : 1,
-    "b" : 1
-  },
-  "EnvQualified:TEST" : {
-     "a" : 2,
-    "b" : 2
-  }
+  ]
 }

Fig.Tests/appsettings.json

@@ -14,14 +14,5 @@
   "Simpsons" :  [
       { "Name" :  "Bart", "Age" :  12},
       { "Name" :  "Homer", "Age" :  35}
-  ],
-
-  "EnvQualified:PROD" : {
-    "a" : 1,
-    "b" : 1
-  },
-  "EnvQualified:TEST" : {
-     "a" : 2,
-    "b" : 2
-  }
+  ]
 }

README.md

@@ -6,6 +6,8 @@ A .NET Standard 2.0 library to help you read application configuration settings
 
 This README is the documentation.
 
+Breaking changes with version 2.0, please read the [Release notes]() carefully before upgrading from an older version.
+
 ## Documentation
 Do you have code like the following sprinkled across your code base?
 
@@ -99,6 +101,25 @@ DbSettings.ConnectionString
 NetworkSettings.TcpPort
 NetworkSettings.Retries
 ```
+## Binding to arrays
+Append indicies to your configuration keys to define an array:
+
+```
+Servers.0 = 10.0.0.1
+Servers.1 = 10.0.0.2
+```
+
+and then bind to a property of type array:
+
+```csharp
+  class MySettings
+  {
+     public string[] Servers { get; set;}
+  }
+```
+Arrays in json files will work this way. See the section below on appsettings.json.
+
+## Variable substitution
 
 ## Binding Validation
 Properties are either required or optional. To make a property optional, assign it a non-null value before binding.
@@ -122,6 +143,7 @@ So given the following class:
 
 the `RefillInterval` and `EnableEspressoMachine` parameters are required while the `Greeting` property is optional.
 
+
 ## Retrieving values by key
 
 For simple applications with just a few parameters defining a custom class could be considered over-engineering. In this case you can retrieve values directly by key, either as strings or converted to a desired type.
@@ -300,7 +322,7 @@ overloads to setup a connection to your database.
 ```
 The SQL query used is `SELECT key, value FROM FigSettings`. You can pass your own query:
 
-```
+```csharp
   var settings = new SettingsBuilder()
    .UseAppSettingsJson("appsettings.json")
    .UseSql<SqlConnection>("ConnectionStrings.SQLiteConnection", "SELECT a,b FROM MySettings")
@@ -314,16 +336,16 @@ lower layers.
 
 ```c#
    var settings = new SettingsBuilder()
+    .UseEnvironmentVariable("ENV")
     .UseAppSettingsJson("appSettings.json")
-    .UseAppSettingsJson("appSettings.${ENV}.json", optional:true)
+    .UseAppSettingsJson("appSettings.${ENV}.json", required:false)
     .UseDotEnv()
-    .UseEnvironmentVariables(prefix: "FIG_", dropPrefix:false)
+    .UseEnvironmentVariables()
     .UseCommandLine(args)    
     .Build<Settings>();
 ```
-Notice the environment specific json file. The variable `${ENV}`
-will be looked up based on what has been added so far:
-environment variables and command line.
+Notice the variable substitution in the second json file. The variable `${ENV}`
+will be looked up in the settings dictionary built so far.
 
 ## Install from nuget
 ```bash
@@ -347,11 +369,11 @@ with keys and values of each layer:
 
 ```
 -------------------- Layer 0 ----------------------
-| Network.ip:TEST        | 127.0.0.1              |
-| Network.port:TEST      | 13001                  |
+| Network.ip             | 127.0.0.1              |
+| Network.port           | 13001                  |
 -------------------- Layer 1 ----------------------
-| Network.ip:PROD        | 10.0.0.1               |
-| Network.port:PROD      | 3001                   |
+| Network.ip             | 10.0.0.1               |
+| Network.port           | 3001                   |
 ---------------------------------------------------
 ```