Updates README and improves samples

README.md

@@ -329,6 +329,36 @@ val es: ErrorStrategies =
 
 
 
+### Multiple Databases
+
+Some applications use multiple databases.
+In that case, it is necessary to have them be different types in the ZIO environment.
+
+Tranzactio offers a typed database class, called `DatabaseT[_]`.
+You only need to provide a different marker type for each database you use.
+
+```scala
+import io.github.gaelrenoux.tranzactio.doobie._
+import javax.sql.DataSource
+import zio._
+
+trait Db1
+trait Db2
+
+val db1Layer: ZLayer[Any, Nothing, DatabaseT[Db1]] = datasource1Layer >>> Database[Db1].fromDatasource
+val db2Layer: ZLayer[Any, Nothing, DatabaseT[Db2]] = datasource2Layer >>> Database[Db2].fromDatasource
+
+val queries1: ZIO[Connection, DbException, List[String]] = ???
+val zio1: ZIO[DatabaseT[Db1], DbException, List[Person]] = DatabaseT[Db1].transactionOrWiden(queries1)
+val zio2: ZIO[DatabaseT[Db2], DbException, List[Person]] = DatabaseT[Db2].transactionOrWiden(queries1)
+```
+
+When creating the layers for the datasources, don't forget to use `.fresh` when you have sub-layers of the same type on both sides!
+
+You can see a full example in the `examples` submodule (in `LayeredAppMultipleDatabases`).
+
+
+
 ### Single-connection Database
 
 In some cases, you might want to have a `Database` module representing a single connection.

examples/src/test/scala/samples/anorm/LayeredAppMultipleDatabases.scala

@@ -1,10 +1,12 @@
 package samples.anorm
 
-import io.github.gaelrenoux.tranzactio.DbException
+import io.github.gaelrenoux.tranzactio.{DbException, ErrorStrategies}
 import io.github.gaelrenoux.tranzactio.anorm._
 import samples.{Conf, ConnectionPool, Person}
 import zio._
 
+import javax.sql.DataSource
+
 /** A sample app where all modules are linked through ZLayer. Should run as is (make sure you have com.h2database:h2 in
  * your dependencies). */
 object LayeredAppMultipleDatabases extends zio.ZIOAppDefault {
@@ -15,19 +17,19 @@ object LayeredAppMultipleDatabases extends zio.ZIOAppDefault {
   /** Marker trait for the second DB */
   trait Db2
 
-  private val database1: ZLayer[Any, Any, DatabaseT[Db1]] = {
+  private val database1: ZLayer[Any, Throwable, DatabaseT[Db1]] = {
     // Fresh calls are required so that the confs and datasource aren't conflated with the other layer's
     val conf = Conf.live("samble-anorm-app-1").fresh
-    val dbRecoveryConf = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
-    val datasource = conf >>> ConnectionPool.live.fresh
+    val dbRecoveryConf: ZLayer[Any, Nothing, ErrorStrategies] = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
+    val datasource: ZLayer[Any, Throwable, DataSource] = conf >>> ConnectionPool.live.fresh
     (datasource ++ dbRecoveryConf) >>> DatabaseT[Db1].fromDatasourceAndErrorStrategies
   }
 
-  private val database2: ZLayer[Any, Any, DatabaseT[Db2]] = {
+  private val database2: ZLayer[Any, Throwable, DatabaseT[Db2]] = {
     // Fresh calls are required so that the confs and datasource aren't conflated with the other layer's
     val conf = Conf.live("samble-anorm-app-2").fresh
-    val dbRecoveryConf = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
-    val datasource = conf >>> ConnectionPool.live.fresh
+    val dbRecoveryConf: ZLayer[Any, Nothing, ErrorStrategies] = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
+    val datasource: ZLayer[Any, Throwable, DataSource] = conf >>> ConnectionPool.live.fresh
     (datasource ++ dbRecoveryConf) >>> DatabaseT[Db2].fromDatasourceAndErrorStrategies
   }
 

examples/src/test/scala/samples/doobie/LayeredAppMultipleDatabases.scala

@@ -1,10 +1,12 @@
 package samples.doobie
 
-import io.github.gaelrenoux.tranzactio.DbException
+import io.github.gaelrenoux.tranzactio.{DbException, ErrorStrategies}
 import io.github.gaelrenoux.tranzactio.doobie._
 import samples.{Conf, ConnectionPool, Person}
 import zio._
 
+import javax.sql.DataSource
+
 /** A sample app with two databases for different set of queries. */
 object LayeredAppMultipleDatabases extends zio.ZIOAppDefault {
 
@@ -14,19 +16,19 @@ object LayeredAppMultipleDatabases extends zio.ZIOAppDefault {
   /** Marker trait for the second DB */
   trait Db2
 
-  private val database1: ZLayer[Any, Any, DatabaseT[Db1]] = {
+  private val database1: ZLayer[Any, Throwable, DatabaseT[Db1]] = {
     // Fresh calls are required so that the confs and datasource aren't conflated with the other layer's
     val conf = Conf.live("samble-doobie-app-1").fresh
-    val dbRecoveryConf = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
-    val datasource = conf >>> ConnectionPool.live.fresh
+    val dbRecoveryConf: ZLayer[Any, Nothing, ErrorStrategies] = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
+    val datasource: ZLayer[Any, Throwable, DataSource] = conf >>> ConnectionPool.live.fresh
     (datasource ++ dbRecoveryConf) >>> DatabaseT[Db1].fromDatasourceAndErrorStrategies
   }
 
-  private val database2: ZLayer[Any, Any, DatabaseT[Db2]] = {
+  private val database2: ZLayer[Any, Throwable, DatabaseT[Db2]] = {
     // Fresh calls are required so that the confs and datasource aren't conflated with the other layer's
     val conf = Conf.live("samble-doobie-app-2").fresh
-    val dbRecoveryConf = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
-    val datasource = conf >>> ConnectionPool.live.fresh
+    val dbRecoveryConf: ZLayer[Any, Nothing, ErrorStrategies] = conf >>> ZLayer.fromFunction((_: Conf).dbRecovery).fresh
+    val datasource: ZLayer[Any, Throwable, DataSource] = conf >>> ConnectionPool.live.fresh
     (datasource ++ dbRecoveryConf) >>> DatabaseT[Db2].fromDatasourceAndErrorStrategies
   }