make Database return PoolStatement

create StatementMethods for common interface between Statement and PoolStatment.

spec/database_spec.cr

@@ -39,4 +39,12 @@ describe DB::Database do
       end
     end
   end
+
+  it "should allow creation of more statements than pool connections" do
+    DB.open "dummy://localhost:1027?initial_pool_size=1&max_pool_size=2" do |db|
+      db.prepare("query1").should be_a(DB::PoolStatement)
+      db.prepare("query2").should be_a(DB::PoolStatement)
+      db.prepare("query3").should be_a(DB::PoolStatement)
+    end
+  end
 end

src/db.cr

@@ -125,6 +125,7 @@ require "./db/database"
 require "./db/driver"
 require "./db/connection"
 require "./db/statement"
+require "./db/pool_statement"
 require "./db/result_set"
 require "./db/error"
 require "./db/mapping"

src/db/database.cr

@@ -54,18 +54,14 @@ module DB
 
     # :nodoc:
     def prepare(query)
-      conn = get_from_pool
-      begin
-        conn.prepare(query)
-      rescue ex
-        return_to_pool(conn)
-        raise ex
-      end
+      # TODO query based cache for pool statement
+      # TODO clear PoolStatements when closing the DB
+      PoolStatement.new self, query
     end
 
     # :nodoc:
-    def get_from_pool
-      @pool.checkout
+    def checkout_some(candidates : Enumerable(Connection)) : {Connection, Bool}
+      @pool.checkout_some candidates
     end
 
     # :nodoc:
@@ -77,7 +73,7 @@ module DB
     # the connection is returned to the pool after
     # when the block ends
     def using_connection
-      connection = get_from_pool
+      connection = @pool.checkout
       begin
         yield connection
       ensure

src/db/pool.cr

@@ -36,6 +36,25 @@ module DB
       resource
     end
 
+    # ```
+    # selected, is_candidate = pool.checkout_some(candidates)
+    # ```
+    # `selected` be a resource from the `candidates` list and `is_candidate` == `true`
+    # or `selected` will be a new resource adn `is_candidate` == `false`
+    def checkout_some(candidates : Enumerable(T)) : {T, Bool}
+      # TODO honor candidates while waiting for availables
+      # this will allow us to remove `candidates.includes?(resource)`
+      candidates.each do |resource|
+        if is_available?(resource)
+          @available.delete resource
+          return {resource, true}
+        end
+      end
+
+      resource = checkout
+      {resource, candidates.includes?(resource)}
+    end
+
     def release(resource : T) : Nil
       if can_increase_idle_pool
         @available << resource

src/db/pool_statement.cr

@@ -0,0 +1,73 @@
+module DB
+  # When a statement is to be executed in a DB that has a connection pool
+  # a statement from the DB needs to be able to represent a statement in any
+  # of the connections of the pool. Otherwise the user will need to deal with
+  # actual connections in some point.
+  class PoolStatement
+    include StatementMethods
+
+    @statements = {} of Connection => Statement
+
+    def initialize(@db : Database, @query : String)
+      # Prepares a statement on some connection
+      # otherwise the preparation is delayed until the first execution.
+      # After the first initialization the connection must be released
+      # it will be checked out when executing it.
+      get_statement.release_connection
+      # TODO use a round-robin selection in the pool so multiple sequentially
+      #      initialized statements are assigned to different connections.
+    end
+
+    protected def do_close
+      # TODO close all statements on all connections.
+      # currently statements are closed when the connection is closed.
+
+      # WHAT-IF the connection is busy? Should each statement be able to
+      # deallocate itself when the connection is free.
+      @statements.clear
+    end
+
+    # See `QueryMethods#exec`
+    def exec : ExecResult
+      get_statement.exec
+    end
+
+    # See `QueryMethods#exec`
+    def exec(*args) : ExecResult
+      get_statement.exec(*args)
+    end
+
+    # See `QueryMethods#exec`
+    def exec(args : Array) : ExecResult
+      get_statement.exec(args)
+    end
+
+    # See `QueryMethods#query`
+    def query : ResultSet
+      get_statement.query
+    end
+
+    # See `QueryMethods#query`
+    def query(*args) : ResultSet
+      get_statement.query(*args)
+    end
+
+    # See `QueryMethods#query`
+    def query(args : Array) : ResultSet
+      get_statement.query(args)
+    end
+
+    # builds a statement over a real connection
+    # the conneciton and the stament is registered in `@statements`
+    private def get_statement : Statement
+      conn, existing = @db.checkout_some(@statements.keys)
+      if existing
+        @statements[conn]
+      else
+        stmt = conn.prepare @query
+        @statements[conn] = stmt
+        stmt
+      end
+    end
+  end
+end

src/db/statement.cr

@@ -1,4 +1,44 @@
 module DB
+  # Common interface for connection based statements
+  # and for connection pool statements.
+  module StatementMethods
+    include Disposable
+
+    protected def do_close
+    end
+
+    # See `QueryMethods#scalar`
+    def scalar(*args)
+      query(*args) do |rs|
+        rs.each do
+          return rs.read
+        end
+      end
+
+      raise "no results"
+    end
+
+    # See `QueryMethods#query`
+    def query(*args)
+      rs = query(*args)
+      yield rs ensure rs.close
+    end
+
+    # See `QueryMethods#exec`
+    abstract def exec : ExecResult
+    # See `QueryMethods#exec`
+    abstract def exec(*args) : ExecResult
+    # See `QueryMethods#exec`
+    abstract def exec(args : Array) : ExecResult
+
+    # See `QueryMethods#query`
+    abstract def query : ResultSet
+    # See `QueryMethods#query`
+    abstract def query(*args) : ResultSet
+    # See `QueryMethods#query`
+    abstract def query(args : Array) : ResultSet
+  end
+
   # Represents a prepared query in a `Connection`.
   # It should be created by `QueryMethods`.
   #
@@ -10,7 +50,7 @@ module DB
   # 4. `#perform_exec` executes a query that is expected to return an `ExecResult`
   # 6. `#do_close` is called to release the statement resources.
   abstract class Statement
-    include Disposable
+    include StatementMethods
 
     # :nodoc:
     getter connection
@@ -18,9 +58,6 @@ module DB
     def initialize(@connection : Connection)
     end
 
-    protected def do_close
-    end
-
     def release_connection
       @connection.database.return_to_pool(@connection)
     end
@@ -41,17 +78,6 @@ module DB
       perform_exec_and_release(args)
     end
 
-    # See `QueryMethods#scalar`
-    def scalar(*args)
-      query(*args) do |rs|
-        rs.each do
-          return rs.read
-        end
-      end
-
-      raise "no results"
-    end
-
     # See `QueryMethods#query`
     def query
       perform_query Tuple.new
@@ -67,12 +93,6 @@ module DB
       perform_query args
     end
 
-    # See `QueryMethods#query`
-    def query(*args)
-      rs = query(*args)
-      yield rs ensure rs.close
-    end
-
     private def perform_exec_and_release(args : Enumerable) : ExecResult
       return perform_exec(args)
     ensure