jonkeane commented on a change in pull request #10601:
URL: https://github.com/apache/arrow/pull/10601#discussion_r658846244



##########
File path: r/R/metadata.R
##########
@@ -56,7 +56,21 @@ apply_arrow_r_metadata <- function(x, r_metadata) {
     if (is.data.frame(x)) {
       if (length(names(x)) && !is.null(columns_metadata)) {
         for (name in intersect(names(columns_metadata), names(x))) {
-          x[[name]] <- apply_arrow_r_metadata(x[[name]], 
columns_metadata[[name]])
+          x[[name]] <- tryCatch({
+            x[[name]] <- apply_arrow_r_metadata(x[[name]], 
columns_metadata[[name]])
+          },
+          error = function(e) {
+            # if we are erroring because of incompatible data, try and make 
this
+            # a tibble
+            # TODO: also check if this is a list?
+            # TODO: only if there are exactly as many sub-list elements as 
rows?
+            # TODO: decide if this obviates the need for the option
+            #   arrow.strucs_as_dfs (or if that is actually a better way to 
handle that)
+            if (grepl("must be compatible with existing data", e$message))
+              x[[name]] <- as.data.frame(x[[name]])
+              class(x[[name]]) <-  c("tbl_df", "tbl", "data.frame")
+              apply_arrow_r_metadata(x[[name]], columns_metadata[[name]])
+          })

Review comment:
       This code chunk will make it so that we can read in data saved in 
parquet files that don't also store the data.frame metadata needed to 
reconstruct them (since until this PR we always stripped that).
   
   If we go this route, we probably should implement the todos listed here and 
also warn that this setup is deprecated.




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