diff --git a/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache b/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache
index d27c5cedbb5..06bbe572734 100644
--- a/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache
+++ b/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache
@@ -69,11 +69,11 @@
     #' @description
     #' Serialize {{{classname}}} to JSON string.
     #'
-    #' @return JSON string reprenation of the {{{classname}}}.
+    #' @return JSON string representation of the {{{classname}}}.
     #' @export
     toJSONString = function() {
       if (!is.null(self$actual_instance)) {
-        self$actual_instance$toJSONString()
+        as.character(jsonlite::minify((self$actual_instance$toJSONString())))
       } else {
         NULL
       }
@@ -83,7 +83,7 @@
     #' @description
     #' Serialize {{{classname}}} to JSON.
     #'
-    #' @return JSON reprenation of the {{{classname}}}.
+    #' @return JSON representation of the {{{classname}}}.
     #' @export
     toJSON = function() {
       if (!is.null(self$actual_instance)) {
@@ -111,6 +111,22 @@
       # no error thrown, restore old values
       self$actual_instance <- actual_instance_bak
       self$actual_type <- actual_type_bak
-    }
+    },
+    #' Returns the string representation of the instance.
+    #'
+    #' @description
+    #' Returns the string representation of the instance.
+    #'
+    #' @return The string representation of the instance.
+    #' @export
+    toString = function() {
+      jsoncontent <- c(
+        sprintf('"actual_instance": %s', if (is.null(self$actual_instance)) {NULL} else {self$actual_instance$toJSONString()}),
+        sprintf('"actual_type": "%s"', self$actual_type),
+        sprintf('"any_of": "%s"',  paste( unlist(self$any_of), collapse=', '))
+      )
+      jsoncontent <- paste(jsoncontent, collapse = ",")
+      as.character(jsonlite::prettify(paste('{', jsoncontent, '}', sep = "")))
+     }
   )
 )
diff --git a/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache b/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache
index d53f32f59fa..20077cccdf8 100644
--- a/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache
+++ b/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache
@@ -84,11 +84,11 @@
     #' @description
     #' Serialize {{{classname}}} to JSON string.
     #'
-    #' @return JSON string reprenation of the {{{classname}}}.
+    #' @return JSON string representation of the {{{classname}}}.
     #' @export
     toJSONString = function() {
       if (!is.null(self$actual_instance)) {
-        self$actual_instance$toJSONString()
+        as.character(jsonlite::minify(self$actual_instance$toJSONString()))
       } else {
         NULL
       }
@@ -98,7 +98,7 @@
     #' @description
     #' Serialize {{{classname}}} to JSON.
     #'
-    #' @return JSON reprenation of the {{{classname}}}.
+    #' @return JSON representation of the {{{classname}}}.
     #' @export
     toJSON = function() {
       if (!is.null(self$actual_instance)) {
@@ -126,6 +126,22 @@
       # no error thrown, restore old values
       self$actual_instance <- actual_instance_bak
       self$actual_type <- actual_type_bak
+    },
+    #' Returns the string representation of the instance.
+    #'
+    #' @description
+    #' Returns the string representation of the instance.
+    #'
+    #' @return The string representation of the instance.
+    #' @export
+    toString = function() {
+      jsoncontent <- c(
+        sprintf('"actual_instance": %s', if (is.null(self$actual_instance)) {NULL} else {self$actual_instance$toJSONString()}),
+        sprintf('"actual_type": "%s"', self$actual_type),
+        sprintf('"one_of": "%s"',  paste( unlist(self$one_of), collapse=', '))
+      )
+      jsoncontent <- paste(jsoncontent, collapse = ",")
+      as.character(jsonlite::prettify(paste('{', jsoncontent, '}', sep = "")))
     }
   )
 )
diff --git a/samples/client/petstore/R/R/any_of_pig.R b/samples/client/petstore/R/R/any_of_pig.R
index 73b8e89c6f9..31044e62b18 100644
--- a/samples/client/petstore/R/R/any_of_pig.R
+++ b/samples/client/petstore/R/R/any_of_pig.R
@@ -92,11 +92,11 @@ AnyOfPig <- R6::R6Class(
     #' @description
     #' Serialize AnyOfPig to JSON string.
     #'
-    #' @return JSON string reprenation of the AnyOfPig.
+    #' @return JSON string representation of the AnyOfPig.
     #' @export
     toJSONString = function() {
       if (!is.null(self$actual_instance)) {
-        self$actual_instance$toJSONString()
+        as.character(jsonlite::minify((self$actual_instance$toJSONString())))
       } else {
         NULL
       }
@@ -106,7 +106,7 @@ AnyOfPig <- R6::R6Class(
     #' @description
     #' Serialize AnyOfPig to JSON.
     #'
-    #' @return JSON reprenation of the AnyOfPig.
+    #' @return JSON representation of the AnyOfPig.
     #' @export
     toJSON = function() {
       if (!is.null(self$actual_instance)) {
@@ -134,7 +134,23 @@ AnyOfPig <- R6::R6Class(
       # no error thrown, restore old values
       self$actual_instance <- actual_instance_bak
       self$actual_type <- actual_type_bak
-    }
+    },
+    #' Returns the string representation of the instance.
+    #'
+    #' @description
+    #' Returns the string representation of the instance.
+    #'
+    #' @return The string representation of the instance.
+    #' @export
+    toString = function() {
+      jsoncontent <- c(
+        sprintf('"actual_instance": %s', if (is.null(self$actual_instance)) {NULL} else {self$actual_instance$toJSONString()}),
+        sprintf('"actual_type": "%s"', self$actual_type),
+        sprintf('"any_of": "%s"',  paste( unlist(self$any_of), collapse=', '))
+      )
+      jsoncontent <- paste(jsoncontent, collapse = ",")
+      as.character(jsonlite::prettify(paste('{', jsoncontent, '}', sep = "")))
+     }
   )
 )
 
diff --git a/samples/client/petstore/R/R/pig.R b/samples/client/petstore/R/R/pig.R
index 565df078209..60f7ecbc002 100644
--- a/samples/client/petstore/R/R/pig.R
+++ b/samples/client/petstore/R/R/pig.R
@@ -108,11 +108,11 @@ Pig <- R6::R6Class(
     #' @description
     #' Serialize Pig to JSON string.
     #'
-    #' @return JSON string reprenation of the Pig.
+    #' @return JSON string representation of the Pig.
     #' @export
     toJSONString = function() {
       if (!is.null(self$actual_instance)) {
-        self$actual_instance$toJSONString()
+        as.character(jsonlite::minify(self$actual_instance$toJSONString()))
       } else {
         NULL
       }
@@ -122,7 +122,7 @@ Pig <- R6::R6Class(
     #' @description
     #' Serialize Pig to JSON.
     #'
-    #' @return JSON reprenation of the Pig.
+    #' @return JSON representation of the Pig.
     #' @export
     toJSON = function() {
       if (!is.null(self$actual_instance)) {
@@ -150,6 +150,22 @@ Pig <- R6::R6Class(
       # no error thrown, restore old values
       self$actual_instance <- actual_instance_bak
       self$actual_type <- actual_type_bak
+    },
+    #' Returns the string representation of the instance.
+    #'
+    #' @description
+    #' Returns the string representation of the instance.
+    #'
+    #' @return The string representation of the instance.
+    #' @export
+    toString = function() {
+      jsoncontent <- c(
+        sprintf('"actual_instance": %s', if (is.null(self$actual_instance)) {NULL} else {self$actual_instance$toJSONString()}),
+        sprintf('"actual_type": "%s"', self$actual_type),
+        sprintf('"one_of": "%s"',  paste( unlist(self$one_of), collapse=', '))
+      )
+      jsoncontent <- paste(jsoncontent, collapse = ",")
+      as.character(jsonlite::prettify(paste('{', jsoncontent, '}', sep = "")))
     }
   )
 )
diff --git a/samples/client/petstore/R/tests/testthat/test_petstore.R b/samples/client/petstore/R/tests/testthat/test_petstore.R
index 424fc5c291a..7db1cc4dcac 100644
--- a/samples/client/petstore/R/tests/testthat/test_petstore.R
+++ b/samples/client/petstore/R/tests/testthat/test_petstore.R
@@ -236,7 +236,10 @@ test_that("Tests oneOf", {
   nested_oneof$nested_pig <- pig
   nested_oneof$size <- 15
   expect_equal(nested_oneof$toJSONString(), '{"size":15,"nested_pig":{"className":"BasquePig","color":"red"}}')
-   
+
+  # test toString
+  expect_equal(as.character(jsonlite::minify(pig$toString())), "{\"actual_instance\":{\"className\":\"BasquePig\",\"color\":\"red\"},\"actual_type\":\"BasquePig\",\"one_of\":\"BasquePig, DanishPig\"}")
+  expect_equal(as.character(jsonlite::minify(Pig$new()$toString())), "{\"one_of\":\"BasquePig, DanishPig\"}")
 })
 
 test_that("Tests anyOf", {