Copy-DbaDbTableData - Exclude generated always columns from the writable destination columns

The period columns of a temporal table and the ledger metadata columns are
GENERATED ALWAYS: not computed, not rowversion, but just as unwritable, and
SMO reports them with Computed = false. The positional mapping counted them,
mapped query columns onto them and the server rejected the insert with error
13536. The lookup is guarded by the version because SMO only supports
GeneratedAlwaysType on SQL Server 2016 and later.

(do Copy-DbaDbTableData)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: andreasjordan

public/Copy-DbaDbTableData.ps1

@@ -56,14 +56,14 @@ function Copy-DbaDbTableData {
         Custom SQL SELECT query to use as the data source instead of copying the entire table or view. Supports 3 or 4-part object names.
         Use this when you need to filter rows, join multiple tables, or transform data during the copy operation. Still requires specifying a Table or View parameter for metadata purposes.
 
-        Note: Columns are mapped by position onto the writable columns of the destination table, so computed and rowversion columns of the destination do not count and must not have a counterpart in the SELECT list.
+        Note: Columns are mapped by position onto the writable columns of the destination table, so computed, rowversion and generated always columns of the destination do not count and must not have a counterpart in the SELECT list.
         If the destination table has an identity column, include a placeholder value (e.g., 0) in your SELECT list at that position.
         The placeholder will be ignored and the identity value auto-generated unless -KeepIdentity is specified.
 
     .PARAMETER ForceExplicitMapping
         When used together with Query parameter, force the use of explicit column mapping (name-based) instead of switching over to ordinal position mapping. Use with care if query contains aliases.
         Default behaviour when using Query parameter is to use ordinal position mapping, due to the possibility of the query including aliases (SELECT x AS y) which could lead to column mismatching and data not copying.
-        Positional mapping skips the computed and rowversion columns of the destination table, so the SELECT list only has to match its writable columns.
+        Positional mapping skips the computed, rowversion and generated always columns of the destination table, so the SELECT list only has to match its writable columns.
 
     .PARAMETER AutoCreateTable
         Automatically creates the destination table if it doesn't exist, using the same structure as the source table.
@@ -673,13 +673,15 @@ function Copy-DbaDbTableData {
                         $bulkCopy.NotifyAfter = $NotifyAfter
                         $bulkCopy.BulkCopyTimeout = $BulkCopyTimeout
 
-                        # Get list of writable columns from destination table to avoid insert failures. Computed and rowversion
-                        # columns cannot be written, and they are also what breaks the implicit positional mapping of SqlBulkCopy:
-                        # it counts a computed column (the server then rejects the insert) and silently drops the source column
-                        # that lands on a rowversion column, shifting every column behind it by one (see #10661).
+                        # Get list of writable columns from destination table to avoid insert failures. Computed, rowversion
+                        # and generated always columns (temporal periods, ledger metadata) cannot be written, and they are also
+                        # what breaks the implicit positional mapping of SqlBulkCopy: it counts a computed column (the server
+                        # then rejects the insert) and silently drops the source column that lands on a rowversion column,
+                        # shifting every column behind it by one (see #10661). GeneratedAlwaysType is only supported by SMO on
+                        # SQL Server 2016 and later, so it has to be guarded by the version.
                         # Refresh the columns collection to ensure it's populated
                         $desttable.Columns.Refresh()
-                        $destColumns = @($desttable.Columns | Where-Object { -not $PSItem.Computed -and $PSItem.DataType.SqlDataType -ne "Timestamp" } | Select-Object -ExpandProperty Name)
+                        $destColumns = @($desttable.Columns | Where-Object { -not $PSItem.Computed -and $PSItem.DataType.SqlDataType -ne "Timestamp" -and -not ($destServer.VersionMajor -ge 13 -and $PSItem.GeneratedAlwaysType -ne "None") } | Select-Object -ExpandProperty Name)
                         Write-Message -Level Verbose -Message "Destination table has $($destColumns.Count) writable columns"
 
                         # The legacy bulk copy library uses a 4 byte integer to track the RowsCopied, so the only option is to use
@@ -712,7 +714,7 @@ function Copy-DbaDbTableData {
                         # Custom queries may have different column names/aliases, so they are mapped by position
                         # Appending -ForceExplicitMapping will override this behaviour and keep explicit column mapping
                         if (-not (Test-Bound -ParameterName Query) -or $ForceExplicitMapping) {
-                            # Map only columns that exist in both source and destination (excluding computed and rowversion columns)
+                            # Map only columns that exist in both source and destination (excluding computed, rowversion and generated always columns)
                             for ($i = 0; $i -lt $reader.FieldCount; $i++) {
                                 $sourceColumn = $reader.GetName($i)
                                 if ($destColumns -contains $sourceColumn) {
@@ -723,9 +725,9 @@ function Copy-DbaDbTableData {
                             }
                         } else {
                             # Map the query columns by position onto the writable destination columns. This is what SqlBulkCopy does
-                            # on its own, except that its list also contains the computed and rowversion columns (see above).
+                            # on its own, except that its list also contains the computed, rowversion and generated always columns (see above).
                             if ($reader.FieldCount -gt $destColumns.Count) {
-                                $columnCountMessage = "The query returns $($reader.FieldCount) columns but $fqtndest has only $($destColumns.Count) writable columns. Computed and rowversion columns cannot be written and do not count."
+                                $columnCountMessage = "The query returns $($reader.FieldCount) columns but $fqtndest has only $($destColumns.Count) writable columns. Computed, rowversion and generated always columns cannot be written and do not count."
                                 $reader.Close()
                                 throw $columnCountMessage
                             }

tests/Copy-DbaDbTableData.Tests.ps1

@@ -217,6 +217,14 @@ Describe $CommandName -Tag IntegrationTests {
     }
 
     Context "When using Query without ForceExplicitMapping and the destination has unwritable columns" {
+        BeforeDiscovery {
+            # GENERATED ALWAYS columns arrived with SQL Server 2016, so the temporal scenario below cannot
+            # be built before that. The value decides a Skip, which Pester needs while it discovers the
+            # tests, so it cannot be read in BeforeAll.
+            $discoveryDestServer = Connect-DbaInstance -SqlInstance $TestConfig.InstanceCopy2
+            $destSupportsTemporal = $discoveryDestServer.VersionMajor -ge 13
+        }
+
         BeforeAll {
             $PSDefaultParameterValues["*-Dba*:EnableException"] = $true
 
@@ -227,6 +235,11 @@ Describe $CommandName -Tag IntegrationTests {
             $null = $destinationDb.Query("CREATE TABLE dbo.dbatoolsci_positional_dest (Id INT, A INT, Computed AS (A * 10), RV ROWVERSION, B INT, C INT)")
             $null = $destinationDb.Query("CREATE TABLE dbo.dbatoolsci_positional_identity (Id INT IDENTITY(1, 1), A INT, B INT, C INT)")
             $null = $destinationDb.Query("CREATE TABLE dbo.dbatoolsci_positional_rowversion (Id INT, A INT, RV ROWVERSION, B INT, C INT)")
+            if ($destinationDb.Parent.VersionMajor -ge 13) {
+                # The period columns of a temporal table are GENERATED ALWAYS: not computed, not rowversion,
+                # but just as unwritable, and interleaved with the writable columns here on purpose.
+                $null = $destinationDb.Query("CREATE TABLE dbo.dbatoolsci_positional_temporal (Id INT PRIMARY KEY, A INT, ValidFrom DATETIME2 GENERATED ALWAYS AS ROW START NOT NULL, B INT, ValidTo DATETIME2 GENERATED ALWAYS AS ROW END NOT NULL, C INT, PERIOD FOR SYSTEM_TIME (ValidFrom, ValidTo)) WITH (SYSTEM_VERSIONING = ON (HISTORY_TABLE = dbo.dbatoolsci_positional_temporal_history))")
+            }
 
             $splatPositional = @{
                 SqlInstance      = $TestConfig.InstanceCopy1
@@ -247,6 +260,13 @@ Describe $CommandName -Tag IntegrationTests {
             $null = $destinationDb.Query("DROP TABLE IF EXISTS dbo.dbatoolsci_positional_dest")
             $null = $destinationDb.Query("DROP TABLE IF EXISTS dbo.dbatoolsci_positional_identity")
             $null = $destinationDb.Query("DROP TABLE IF EXISTS dbo.dbatoolsci_positional_rowversion")
+            $destinationDb.Tables.Refresh()
+            if ($destinationDb.Tables | Where-Object Name -eq "dbatoolsci_positional_temporal") {
+                # System versioning has to be turned off before the temporal table can be dropped.
+                $null = $destinationDb.Query("ALTER TABLE dbo.dbatoolsci_positional_temporal SET (SYSTEM_VERSIONING = OFF)")
+                $null = $destinationDb.Query("DROP TABLE dbo.dbatoolsci_positional_temporal")
+                $null = $destinationDb.Query("DROP TABLE IF EXISTS dbo.dbatoolsci_positional_temporal_history")
+            }
 
             $PSDefaultParameterValues.Remove("*-Dba*:EnableException")
         }
@@ -277,6 +297,22 @@ Describe $CommandName -Tag IntegrationTests {
             $destData.C | Should -Be @(33, 333)
         }
 
+        It "Does not count the generated always columns of a temporal destination" -Skip:(-not $destSupportsTemporal) {
+            # The period columns are GENERATED ALWAYS, so the server refuses explicit values for them.
+            # A positional mapping that counts them maps writable source columns onto them and fails.
+            $splatTemporal = $splatPositional.Clone()
+            $splatTemporal.DestinationTable = "dbatoolsci_positional_temporal"
+            $result = Copy-DbaDbTableData @splatTemporal
+            $WarnVar | Should -BeNullOrEmpty
+            $result.RowsCopied | Should -Be 2
+
+            $destData = $destinationDb.Query("SELECT Id, A, ValidFrom, B, ValidTo, C FROM dbo.dbatoolsci_positional_temporal ORDER BY Id")
+            $destData.A | Should -Be @(11, 111)
+            $destData.B | Should -Be @(22, 222)
+            $destData.C | Should -Be @(33, 333)
+            $destData.ValidFrom | Should -Not -BeNullOrEmpty
+        }
+
         It "Still ignores the identity placeholder unless KeepIdentity is used" {
             $splatIdentity = $splatPositional.Clone()
             $splatIdentity.Query = "SELECT 0, A, B, C FROM dbo.dbatoolsci_positional_source ORDER BY Id"