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Fix alter column type JSON to nVarchar #38464

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0cdb004
Fix alter column type JSON to nVarchar
atiq-bs23 Jun 19, 2026
c74ddb1
Feedback resolve - pr comment
atiq-bs23 Jun 20, 2026
c478d20
PR feedback resolve - integration test
atiq-bs23 Jun 20, 2026
1f5d54a
Fix - Copy annotations and Comment to replacement column in AlterColu…
atiq-bs23 Jun 20, 2026
bcc45aa
comment updated
atiq-bs23 Jun 20, 2026
5e49aeb
Merge branch 'dotnet:main' into fix-json-to-nvarchar-column-migration
atiq-bs23 Jun 21, 2026
6624934
Merge remote-tracking branch 'origin/main' into fix-json-to-nvarchar-…
atiq-bs23 Jun 21, 2026
b24bf1a
Merge branch 'fix-json-to-nvarchar-column-migration' of https://githu…
atiq-bs23 Jun 21, 2026
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177 changes: 140 additions & 37 deletions src/EFCore.SqlServer/Migrations/SqlServerMigrationsSqlGenerator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -294,6 +294,7 @@ protected override void Generate(

var narrowed = false;
var oldColumnSupported = IsOldColumnSupported(model);
string? oldType = null;

// SQL Server can't ALTER COLUMN on a computed column when the expression is unchanged; see #33425.
var computedColumnIsNoOp = operation.ComputedColumnSql != null
Expand All @@ -308,7 +309,7 @@ protected override void Generate(
throw new InvalidOperationException(SqlServerStrings.AlterIdentityColumn);
}

var oldType = operation.OldColumn.ColumnType
oldType = operation.OldColumn.ColumnType
?? GetColumnType(
operation.Schema,
operation.Table,
Expand Down Expand Up @@ -429,43 +430,17 @@ protected override void Generate(

if (alterStatementNeeded)
{
builder
.Append("ALTER TABLE ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
.Append(" ALTER COLUMN ");

// NB: ComputedColumnSql, IsStored, DefaultValue, DefaultValueSql, Comment, ValueGenerationStrategy, and Identity are
// handled elsewhere. Don't copy them here.
var definitionOperation = new AlterColumnOperation
// SQL Server can't ALTER COLUMN from json to a non JSON type; use rename-add-copy-drop instead. See #38364.
if ((oldType ?? operation.OldColumn.ColumnType)
?.Equals("json", StringComparison.OrdinalIgnoreCase) == true
&& !columnType.Equals("json", StringComparison.OrdinalIgnoreCase))
{
Schema = operation.Schema,
Table = operation.Table,
Name = operation.Name,
ClrType = operation.ClrType,
ColumnType = operation.ColumnType,
IsUnicode = operation.IsUnicode,
IsFixedLength = operation.IsFixedLength,
MaxLength = operation.MaxLength,
Precision = operation.Precision,
Scale = operation.Scale,
IsRowVersion = operation.IsRowVersion,
IsNullable = operation.IsNullable,
Collation = operation.Collation,
OldColumn = operation.OldColumn
};
definitionOperation.AddAnnotations(
operation.GetAnnotations().Where(a => a.Name != SqlServerAnnotationNames.ValueGenerationStrategy
&& a.Name != SqlServerAnnotationNames.Identity));

ColumnDefinition(
operation.Schema,
operation.Table,
operation.Name,
definitionOperation,
model,
builder);

builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
AlterColumnFromJson(operation, columnType, model, builder);
}
else
{
AppendAlterColumnDefinition(operation, operation.IsNullable, model, builder);
}
}

if (!Equals(operation.DefaultValue, oldDefaultValue) || operation.DefaultValueSql != oldDefaultValueSql)
Expand Down Expand Up @@ -514,6 +489,134 @@ protected override void Generate(
builder.EndCommand(suppressTransaction: IsMemoryOptimized(operation, model, operation.Schema, operation.Table));
}

private void AlterColumnFromJson(
AlterColumnOperation operation,
string columnType,
IModel? model,
MigrationCommandListBuilder builder)
{
var tempColumnName = "ef_temp_" + operation.Name;

Rename(
Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema)
+ "."
+ Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name),
tempColumnName,
"COLUMN",
builder);

builder
.Append("ALTER TABLE ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
.Append(" ADD ");

var addColumnOperation = new AddColumnOperation
{
Schema = operation.Schema,
Table = operation.Table,
Name = operation.Name,
ClrType = operation.ClrType,
ColumnType = operation.ColumnType,
IsUnicode = operation.IsUnicode,
IsFixedLength = operation.IsFixedLength,
MaxLength = operation.MaxLength,
Precision = operation.Precision,
Scale = operation.Scale,
IsRowVersion = operation.IsRowVersion,
IsNullable = true,
Collation = operation.Collation,
Comment = operation.Comment
};
addColumnOperation.AddAnnotations(
operation.GetAnnotations().Where(a => a.Name != SqlServerAnnotationNames.Identity));

ColumnDefinition(
operation.Schema,
operation.Table,
operation.Name,
addColumnOperation,
model,
builder);

builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);

var updateSql = new StringBuilder()
.Append("UPDATE ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
.Append(" SET ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Name))
.Append(" = CONVERT(")
.Append(columnType)
.Append(", ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(tempColumnName))
.Append(")")
.ToString();

builder
.Append("EXEC(N'")
.Append(updateSql.Replace("'", "''"))
.Append("')");

builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);

builder
.Append("ALTER TABLE ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
.Append(" DROP COLUMN ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(tempColumnName))
.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);

if (!operation.IsNullable)
{
AppendAlterColumnDefinition(operation, false, model, builder);
}
}

private void AppendAlterColumnDefinition(
AlterColumnOperation operation,
bool isNullable,
IModel? model,
MigrationCommandListBuilder builder)
{
builder
.Append("ALTER TABLE ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
.Append(" ALTER COLUMN ");

// NB: ComputedColumnSql, IsStored, DefaultValue, DefaultValueSql, Comment, ValueGenerationStrategy, and Identity are
// handled elsewhere. Don't copy them here.
var definitionOperation = new AlterColumnOperation
{
Schema = operation.Schema,
Table = operation.Table,
Name = operation.Name,
ClrType = operation.ClrType,
ColumnType = operation.ColumnType,
IsUnicode = operation.IsUnicode,
IsFixedLength = operation.IsFixedLength,
MaxLength = operation.MaxLength,
Precision = operation.Precision,
Scale = operation.Scale,
IsRowVersion = operation.IsRowVersion,
IsNullable = isNullable,
Collation = operation.Collation,
OldColumn = operation.OldColumn
};
definitionOperation.AddAnnotations(
operation.GetAnnotations().Where(a => a.Name != SqlServerAnnotationNames.ValueGenerationStrategy
&& a.Name != SqlServerAnnotationNames.Identity));

ColumnDefinition(
operation.Schema,
operation.Table,
operation.Name,
definitionOperation,
model,
builder);

builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
}

/// <summary>
/// Builds commands for the given <see cref="RenameIndexOperation" />
/// by making calls on the given <see cref="MigrationCommandListBuilder" />.
Expand Down
68 changes: 68 additions & 0 deletions test/EFCore.SqlServer.FunctionalTests/Migrations/MigrationsSqlServerTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1599,6 +1599,74 @@ public override async Task Convert_string_column_to_a_json_column_containing_col
AssertSql();
}

[ConditionalFact(typeof(SqlServerTestEnvironment), nameof(SqlServerTestEnvironment.IsJsonTypeSupported))]
public virtual async Task Convert_json_column_back_to_string_column()
{
// Use explicit operation rather than model diffing: the snapshot round-trip of a source model
// with HasColumnType("json") does not reliably preserve identity annotations, causing the
// model differ to emit a spurious AlterColumnOperation for the PK that hits the identity check.
await Test(
builder =>
{
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builder.Entity(
"Entity", e =>
{
e.Property<int>("Id").ValueGeneratedNever();
e.HasKey("Id");
e.Property<string>("Name").HasColumnType("json");
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});
},
new MigrationOperation[]
{
new AlterColumnOperation
{
Table = "Entity",
Name = "Name",
ClrType = typeof(string),
ColumnType = "nvarchar(450)",
IsNullable = true,
OldColumn = new AddColumnOperation
{
ClrType = typeof(string),
ColumnType = "json",
IsNullable = true
}
},
new CreateIndexOperation
{
Table = "Entity",
Name = "IX_Entity_Name",
Columns = new[] { "Name" }
}
},
model =>
{
var table = Assert.Single(model.Tables);
var column = Assert.Single(table.Columns, c => c.Name == "Name");
Assert.Equal("nvarchar(450)", column.StoreType);
Assert.True(column.IsNullable);
var index = Assert.Single(table.Indexes);
Assert.Contains(column, index.Columns);
});

AssertSql(
"""
DECLARE @var nvarchar(max);
SELECT @var = QUOTENAME(OBJECT_NAME([c].[default_object_id]))
FROM [sys].[columns] [c]
WHERE [c].[object_id] = OBJECT_ID(N'[Entity]') AND [c].[name] = N'Name';
IF @var IS NOT NULL EXEC(N'ALTER TABLE [Entity] DROP CONSTRAINT ' + @var + ';');
EXEC sp_rename N'[Entity].[Name]', N'ef_temp_Name', 'COLUMN';
ALTER TABLE [Entity] ADD [Name] nvarchar(450) NULL;
EXEC(N'UPDATE [Entity] SET [Name] = CONVERT(nvarchar(450), [ef_temp_Name])');
ALTER TABLE [Entity] DROP COLUMN [ef_temp_Name];
""",
//
"""
CREATE INDEX [IX_Entity_Name] ON [Entity] ([Name]);
""");
}

[Fact]
public virtual async Task Alter_column_make_required_with_index_with_included_properties()
{
Expand Down
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