Refine single-column Table to act as a Column

distribution/lib/Standard/Database/0.0.0-dev/src/Connection/Connection.enso

@@ -547,8 +547,9 @@ private _make_table_for_name connection name alias internal_temporary_keep_alive
            warning. We do not want to fail, as we do want to allow the user to
            access any table already present in the database.
         DB_Table_Module.make_table connection name columns ctx on_problems=Problem_Behavior.Report_Warning
-    result.catch SQL_Error _->
+    if result.is_error then
         Error.throw (Table_Not_Found.Error name)
+    result
 
 ## PRIVATE
 private _check_statement_is_allowed connection stmt =

distribution/lib/Standard/Database/0.0.0-dev/src/DB_Column.enso

@@ -96,7 +96,7 @@ type DB_Column
        Converts this column into a single-column table.
     to_table : DB_Table
     to_table self =
-        DB_Table.Value self.name self.connection [self.as_internal] self.context
+        DB_Table.new self.name self.connection [self.as_internal] self.context
 
     ## ALIAS column type, field info, metadata
        GROUP Standard.Base.Metadata

distribution/lib/Standard/Database/0.0.0-dev/src/DB_Table.enso

@@ -68,6 +68,7 @@ import project.Internal.IR.Query.Query
 import project.Internal.IR.SQL_Expression.SQL_Expression
 import project.Internal.IR.SQL_Join_Kind.SQL_Join_Kind
 import project.Internal.SQL_Type_Reference.SQL_Type_Reference
+import project.Internal.Type_Refinements.DB_Table_Refinements
 import project.SQL_Query.SQL_Query
 import project.SQL_Statement.SQL_Statement
 import project.SQL_Type.SQL_Type
@@ -80,9 +81,8 @@ polyglot java import java.util.UUID
 
 ## Represents a column-oriented table data structure backed by a database.
 type DB_Table
-    ## PRIVATE
-
-       Represents a column-oriented table data structure backed by a database.
+    ## Internal constructor that should not be used directly.
+       Please use `DB_Table.new` instead.
 
        Arguments:
        - internal_name: The name of the table.
@@ -91,6 +91,14 @@ type DB_Table
        - context: The context associated with this table.
     private Value internal_name:Text connection:(Connection | Any) (internal_columns:(Vector Internal_Column)) context:Context
 
+    ## The internal constructor used to construct a DB_Table instance.
+
+       It can perform some additional operations, like refining the type,
+       so it should always be preferred over calling `DB_Table.Value` directly.
+    private new (internal_name:Text) connection:(Connection | Any) (internal_columns:(Vector Internal_Column)) context:Context -> DB_Table =
+        DB_Table_Refinements.refine_table <|
+            DB_Table.Value internal_name connection internal_columns context
+
     ## GROUP Standard.Base.Metadata
        ICON metadata
        The name of the table.
@@ -1648,7 +1656,7 @@ type DB_Table
             problem_builder.attach_problems_before on_problems <|
                 new_from = From_Spec.Join sql_join_kind left_setup.subquery right_setup.subquery on_expressions
                 new_ctx = Context.for_subquery new_from . set_where_filters where_expressions
-                DB_Table.Value new_table_name self.connection result_columns new_ctx
+                DB_Table.new new_table_name self.connection result_columns new_ctx
 
     ## ALIAS append, cartesian join
        GROUP Standard.Base.Calculations
@@ -2067,7 +2075,7 @@ type DB_Table
                             input_column = Internal_Column.Value name (infer_return_type expression) expression
                             dialect.adapt_unified_column input_column result_type infer_return_type
 
-                        DB_Table.Value union_alias self.connection new_columns new_ctx
+                        DB_Table.new union_alias self.connection new_columns new_ctx
 
     ## ALIAS average, count, count distinct, first, group by, last, longest, maximum, mean, median, minimum, mode, percentile, shortest, standard deviation, sum, summarize, variance
        GROUP Standard.Base.Calculations
@@ -2805,7 +2813,7 @@ type DB_Table
        Arguments:
        - columns: The columns with which to update this table.
     updated_columns : Vector Internal_Column -> DB_Table
-    updated_columns self internal_columns = DB_Table.Value self.name self.connection internal_columns self.context
+    updated_columns self internal_columns = DB_Table.new self.name self.connection internal_columns self.context
 
     ## PRIVATE
 
@@ -2814,7 +2822,7 @@ type DB_Table
        Arguments:
        - ctx: The new context for this table.
     updated_context : Context -> DB_Table
-    updated_context self ctx = DB_Table.Value self.name self.connection self.internal_columns ctx
+    updated_context self ctx = DB_Table.new self.name self.connection self.internal_columns ctx
 
     ## PRIVATE
 
@@ -2838,9 +2846,9 @@ type DB_Table
             setup = ctx.as_subquery self.name [internal_columns]
             new_ctx = Context.for_subquery setup.subquery
             new_columns = setup.new_columns.first
-            DB_Table.Value self.name self.connection new_columns new_ctx
+            DB_Table.new self.name self.connection new_columns new_ctx
         False ->
-            DB_Table.Value self.name self.connection internal_columns ctx
+            DB_Table.new self.name self.connection internal_columns ctx
 
     ## PRIVATE
        Nests a table as a subquery, using `updated_context_and_columns`, which
@@ -2926,10 +2934,11 @@ type DB_Table
 
          - `Auto_Detect`: The file format is determined by the provided file.
          - `Bytes` and `Plain_Text`: The Table does not support these types in
-            the `write` function. If passed as format, an
-            `Illegal_Argument` is raised. To write out the table as plain
-            text, the user needs to call the `Text.from Table` method and then
-            use the `Text.write` function.
+           the `write` function. If passed as format, an
+           `Illegal_Argument` is raised. To write out the table as plain
+           text, the user needs to convert the Table to Text
+           (e.g. using `to_delimited` method) and then use the `Text.write`
+           function.
 
        > Example
          Write a database table to a CSV file.
@@ -3216,7 +3225,7 @@ make_table connection table_name columns ctx on_problems =
         problem_builder.report_unique_name_strategy column_names_validator
         # We do not want to stop the table from being fetched, so we report the issues as warnings.
         problem_builder.attach_problems_before on_problems <|
-            DB_Table.Value table_name connection cols ctx
+            DB_Table.new table_name connection cols ctx
 
 ## PRIVATE
    By default, join on the first column, unless it's a cross join, in which
@@ -3276,7 +3285,7 @@ make_literal_table connection column_vectors column_names alias =
                 if needs_cast.not then base_column else
                     connection.dialect.make_cast base_column sql_type infer_type_from_database
 
-            DB_Table.Value alias connection internal_columns context
+            DB_Table.new alias connection internal_columns context
 
 ## PRIVATE
 Many_Files_List.from (that : DB_Table) =

distribution/lib/Standard/Database/0.0.0-dev/src/Internal/Common/Lookup_Query_Helper.enso

@@ -57,7 +57,7 @@ build_lookup_query base_table lookup_table key_columns add_new_columns allow_unm
         new_ctx_with_invariant_check = new_ctx.add_where_filters [make_invariant_check subquery_setup.lookup_counter allow_unmatched_rows]
 
         precheck_for_duplicate_matches lookup_columns subquery_setup base_table.connection new_ctx <|
-            DB_Table.Value subquery_setup.new_table_name base_table.connection new_columns new_ctx_with_invariant_check
+            DB_Table.new subquery_setup.new_table_name base_table.connection new_columns new_ctx_with_invariant_check
 
 ## PRIVATE
    Checks if they key contains NULL values or if there would be unmatched rows
@@ -196,7 +196,7 @@ precheck_for_duplicate_matches lookup_columns subquery_setup connection new_ctx
     key_columns_for_duplicate_check = (_.flatten) <| lookup_columns.map_with_index ix-> c-> case c of
         Lookup_Column.Key_Column _ _ -> [subquery_setup.get_self_column ix]
         _ -> []
-    table_for_duplicate_check = DB_Table.Value subquery_setup.new_table_name connection [subquery_setup.lookup_counter]+key_columns_for_duplicate_check new_ctx
+    table_for_duplicate_check = DB_Table.new subquery_setup.new_table_name connection [subquery_setup.lookup_counter]+key_columns_for_duplicate_check new_ctx
     duplicate_lookup_matches = table_for_duplicate_check.filter 0 (Filter_Condition.Greater than=1) . read (..First 1)
     case duplicate_lookup_matches.row_count > 0 of
         True ->

distribution/lib/Standard/Database/0.0.0-dev/src/Internal/Type_Refinements/DB_Table_Refinements.enso

@@ -0,0 +1,15 @@
+private
+
+from Standard.Base import all
+
+import project.DB_Column.DB_Column
+import project.DB_Table.DB_Table
+from project.Internal.Type_Refinements.Single_Column_DB_Table_Conversions import all
+
+refine_table (table : DB_Table) =
+    if is_single_column table . not then table else
+        r = table : DB_Table & DB_Column
+        r
+
+is_single_column table:DB_Table -> Boolean =
+    table.column_count == 1

distribution/lib/Standard/Database/0.0.0-dev/src/Internal/Type_Refinements/Single_Column_DB_Table_Conversions.enso

@@ -0,0 +1,12 @@
+private
+
+from Standard.Base import all
+
+import project.DB_Column.DB_Column
+import project.DB_Table.DB_Table
+from project.Internal.Type_Refinements.DB_Table_Refinements import is_single_column
+
+## This conversion is internal and should never be exported.
+DB_Column.from (that : DB_Table) -> DB_Column =
+    Runtime.assert (is_single_column that)
+    that.at 0

distribution/lib/Standard/Table/0.0.0-dev/src/Column.enso

@@ -27,6 +27,7 @@ import project.Internal.Offset_Helper
 import project.Internal.Parse_Values_Helper
 import project.Internal.Read_Many_Helpers
 import project.Internal.Storage
+import project.Internal.Type_Refinements.Column_Refinements
 import project.Internal.Value_Type_Helpers
 import project.Internal.Widget_Helpers
 import project.Fill_With.Fill_With
@@ -38,7 +39,7 @@ from project.Errors import Conversion_Failure, Inexact_Type_Coercion, Invalid_Co
 from project.Internal.Column_Format import all
 from project.Internal.Java_Exports import make_string_builder
 from project.Internal.Storage import enso_to_java, java_to_enso
-from project.Internal.Type_Refinements.Single_Value_Column import refine_with_single_value
+from project.Table import from_java_table
 
 polyglot java import org.enso.base.Time_Utils
 polyglot java import org.enso.table.data.column.operation.cast.CastProblemAggregator
@@ -142,7 +143,7 @@ type Column
        Creates a new column given a Java Column object.
     from_java_column java_column:Java_Column -> Column =
         column = Column.Value java_column
-        column |> refine_with_single_value
+        Column_Refinements.refine_column column
 
     ## PRIVATE
        ADVANCED
@@ -160,12 +161,16 @@ type Column
             Column.from_java_column java_column
 
     ## PRIVATE
-
-       A representation of a column in a Table.
+       Internal constructor that should not be used directly.
+       Please use `from_java_column` instead.
 
        Arguments:
-       - java_column: The internal representation of the column.
-    private Value java_column
+       - internal_java_column: The internal representation of the column.
+    private Value internal_java_column
+
+    ## PRIVATE
+       A getter that is a workaround for bug https://github.com/enso-org/enso/issues/12180
+    private java_column self = self.internal_java_column
 
     ## PRIVATE
        ADVANCED
@@ -2396,7 +2401,7 @@ type Column
 
              example_to_table = Examples.integer_column.to_table
     to_table : Table
-    to_table self = Table.Value self.java_column.toTable
+    to_table self = from_java_table self.java_column.toTable
 
     ## ALIAS column type, field info, metadata
        GROUP Standard.Base.Metadata

distribution/lib/Standard/Table/0.0.0-dev/src/Excel/Excel_Workbook.enso

@@ -34,6 +34,7 @@ import project.Table.Table
 from project.Errors import Empty_Sheet, No_Rows
 from project.Internal.Excel_Reader import handle_invalid_location
 from project.Internal.Table_Helpers import duplicate_rows
+from project.Table import from_java_table
 
 polyglot java import java.io.File as Java_File
 polyglot java import org.apache.poi.ss.usermodel.Workbook
@@ -244,7 +245,7 @@ type Excel_Workbook
                     names = self.sheet_names
                     if (query < 1 || query >= names.length) then Error.throw (Illegal_Argument.Error "Worksheet index out of range (1 - "+names.length.to_text+").") else
                         ExcelReader.readRangeByName java_workbook (names.at (query - 1)) java_headers skip_rows java_limit java_problem_aggregator
-        limit.attach_warning (Table.Value java_table)
+        limit.attach_warning (from_java_table java_table)
 
     ## PRIVATE
        GROUP Standard.Base.Input
@@ -269,15 +270,15 @@ type Excel_Workbook
                 java_table = Java_Problems.with_problem_aggregator Problem_Behavior.Report_Warning java_problem_aggregator->
                     self.with_java_workbook java_workbook->
                         ExcelReader.readRangeByName java_workbook sheet_name java_headers skip_rows java_limit java_problem_aggregator
-                row_limit.attach_warning (Table.Value java_table)
+                row_limit.attach_warning (from_java_table java_table)
             Excel_Section.Cell_Range address headers skip_rows row_limit ->
                 java_headers = Excel_Reader.make_java_headers headers
                 java_limit = row_limit.rows_to_read
                 java_table = Java_Problems.with_problem_aggregator Problem_Behavior.Report_Warning java_problem_aggregator->
                     self.with_java_workbook java_workbook-> case address of
                         _ : Excel_Range -> ExcelReader.readRange java_workbook address.java_range java_headers skip_rows java_limit java_problem_aggregator
                         _ : Text -> ExcelReader.readRangeByName java_workbook address java_headers skip_rows java_limit java_problem_aggregator
-                row_limit.attach_warning (Table.Value java_table)
+                row_limit.attach_warning (from_java_table java_table)
 
     ## PRIVATE
        GROUP Standard.Base.Input

distribution/lib/Standard/Table/0.0.0-dev/src/Internal/Delimited_Reader.enso

@@ -12,6 +12,7 @@ import project.Internal.Java_Problems
 import project.Rows_To_Read.Rows_To_Read
 import project.Table.Table
 from project.Errors import Empty_File_Error, Mismatched_Quote, Parser_Error
+from project.Table import from_java_table
 
 polyglot java import com.univocity.parsers.common.TextParsingException
 polyglot java import java.io.InputStream
@@ -98,7 +99,7 @@ read_from_reader format java_reader on_problems:Problem_Behavior max_columns=409
         Java_Problems.with_problem_aggregator on_problems java_problem_aggregator->
             reader = prepare_reader format max_columns on_problems java_problem_aggregator
             java_table = reader.read java_reader
-            format.row_limit.attach_warning (Table.Value java_table)
+            format.row_limit.attach_warning (from_java_table java_table)
 
 ## PRIVATE
 prepare_reader format:Delimited_Format max_columns on_problems:Problem_Behavior java_problem_aggregator newline_override=Nothing =

distribution/lib/Standard/Table/0.0.0-dev/src/Internal/Delimited_Writer.enso

@@ -14,6 +14,7 @@ import project.Internal.Java_Problems
 import project.Match_Columns.Match_Columns
 import project.Table.Table
 from project.Errors import Column_Count_Mismatch, Column_Name_Mismatch
+from project.Table import from_java_table
 
 polyglot java import java.io.IOException
 polyglot java import java.io.PrintWriter
@@ -94,7 +95,7 @@ append_to_local_file table format (file : File) match_columns on_problems:Proble
                     Error.throw (Illegal_Argument.Error "Cannot append by name when headers are not present in the existing data.")
                 Match_Columns.By_Position ->
                     ColumnMapper.mapColumnsByPosition table.java_table column_count
-        reordered_table = Table.Value reordered_java_table
+        reordered_table = from_java_table reordered_java_table
         writing_new_file = preexisting_headers == Nothing
         amended_format_1 = case writing_new_file && (should_write_headers format.headers) of
             True -> format.with_headers

distribution/lib/Standard/Table/0.0.0-dev/src/Internal/Excel_Reader.enso

@@ -11,6 +11,7 @@ import project.Internal.Excel_Section.Excel_Section
 import project.Internal.Java_Problems
 import project.Table.Table
 from project.Errors import Duplicate_Output_Column_Names, Empty_Sheet, Invalid_Column_Names, Invalid_Location
+from project.Table import from_java_table
 
 polyglot java import java.io.File as Java_File
 polyglot java import org.apache.poi.poifs.filesystem.NotOLE2FileException
@@ -60,14 +61,14 @@ read_file file section on_problems:Problem_Behavior xls_format=False =
                 java_table = case sheet of
                     _ : Integer -> ExcelReader.readSheetByIndex java_file sheet (make_java_headers headers) skip_rows java_limit file_format java_problem_aggregator
                     _ : Text -> ExcelReader.readSheetByName java_file sheet (make_java_headers headers) skip_rows java_limit file_format java_problem_aggregator
-                row_limit.attach_warning (Table.Value java_table)
+                row_limit.attach_warning (from_java_table java_table)
         Excel_Section.Cell_Range address headers skip_rows row_limit ->
             Java_Problems.with_problem_aggregator on_problems java_problem_aggregator->
                 java_limit = row_limit.rows_to_read
                 java_table = case address of
                     _ : Excel_Range -> ExcelReader.readRange java_file address.java_range (make_java_headers headers) skip_rows java_limit file_format java_problem_aggregator
                     _ : Text -> ExcelReader.readRangeByName java_file address (make_java_headers headers) skip_rows java_limit file_format java_problem_aggregator
-                row_limit.attach_warning (Table.Value java_table)
+                row_limit.attach_warning (from_java_table java_table)
 
     handle_reader file reader
 

distribution/lib/Standard/Table/0.0.0-dev/src/Internal/Read_Many_Helpers.enso

@@ -77,26 +77,26 @@ _merge_input_and_tables (input_table : Table) (tables_for_rows : Vector Read_Man
 
         multiplicated_inputs = duplicate_rows input_table counts
         Runtime.assert (unified_data.row_count == multiplicated_inputs.row_count)
-        Runtime.assert (unified_metadata.is_nothing || (unified_metadata.row_count == unified_data.row_count))
+        Runtime.assert ((Nothing == unified_metadata) || (unified_metadata.row_count == unified_data.row_count))
 
-        first_pass = if unified_metadata.is_nothing then multiplicated_inputs else
+        first_pass = if Nothing == unified_metadata then multiplicated_inputs else
             multiplicated_inputs.zip unified_metadata right_prefix=""
         first_pass.zip unified_data right_prefix=""
 
 ## Unifies provided metadata tables, knowing that some tables may have no 
    metadata - in such case we want to insert as many Nothing rows for metadata 
    as there are rows in the corresponding data table.
 _unify_metadata (tables : Vector Read_Many_As_Table_Result) (on_problems : Problem_Behavior) -> Table | Nothing =
-    has_no_metadata = tables.all r-> r.metadata.is_nothing
+    has_no_metadata = tables.all r-> Nothing == r.metadata
     if has_no_metadata then Nothing else
         unique = Column_Naming_Helper.in_memory.create_unique_name_strategy
         tables.each r->
-            if r.metadata.is_nothing.not then unique.mark_used r.metadata.column_names
+            if Nothing != r.metadata then unique.mark_used r.metadata.column_names
 
         # A dummy column because we cannot create a table with 0 columns, it will be removed after union. We find an unique name for it to avoid conflicts.
         dummy_column_name = unique.make_unique "_Internal_Placeholder_Column_"
         tables_for_union = tables.map r->
-            if r.metadata.is_nothing.not then r.metadata else
+            if Nothing != r.metadata then r.metadata else
                 Table.new [Column.from_repeated_item dummy_column_name Nothing r.data.row_count]
 
         # Metadata are always merged by-name and columns that appear only in some tables are kept.