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Fix alter column type JSON to nVarchar #38464

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Fix alter column type JSON to nVarchar #38464

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184 changes: 150 additions & 34 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 +430,158 @@ protected override void Generate(

if (alterStatementNeeded)
{
builder
.Append("ALTER TABLE ")
.Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(operation.Table, operation.Schema))
.Append(" ALTER COLUMN ");
// SQL Server can't ALTER COLUMN from json to a character type; use rename-add-copy-drop instead. See #38364.
if ((oldType ?? operation.OldColumn.ColumnType)
?.Equals("json", StringComparison.OrdinalIgnoreCase) == true
&& !columnType.Equals("json", StringComparison.OrdinalIgnoreCase))
Comment on lines +433 to +436
{
var tempColumnName = "ef_temp_" + operation.Name;

@AndriySvyryd AndriySvyryd Jun 19, 2026

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Extract the logic in this block to a method to improve readability


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 ");

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

Comment on lines +453 to +475
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);

// NB: ComputedColumnSql, IsStored, DefaultValue, DefaultValueSql, Comment, ValueGenerationStrategy, and Identity are
// handled elsewhere. Don't copy them here.
var definitionOperation = new AlterColumnOperation
if (!operation.IsNullable)
{
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 = false,
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);
}
}
else
{
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));
builder

@AndriySvyryd AndriySvyryd Jun 19, 2026

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Extract the logic in this block and call it from the if block above

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

ColumnDefinition(
operation.Schema,
operation.Table,
operation.Name,
definitionOperation,
model,
builder);
// 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 = operation.IsNullable,
Collation = operation.Collation,
OldColumn = operation.OldColumn
};
definitionOperation.AddAnnotations(
operation.GetAnnotations().Where(a => a.Name != SqlServerAnnotationNames.ValueGenerationStrategy
&& a.Name != SqlServerAnnotationNames.Identity));

builder.AppendLine(Dependencies.SqlGenerationHelper.StatementTerminator);
ColumnDefinition(
operation.Schema,
operation.Table,
operation.Name,
definitionOperation,
model,
builder);

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

if (!Equals(operation.DefaultValue, oldDefaultValue) || operation.DefaultValueSql != oldDefaultValueSql)
Expand Down
53 changes: 53 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 +1599,59 @@ 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 =>
{
Comment thread
AndriySvyryd marked this conversation as resolved.
builder.Entity(
"Entity", e =>
{
e.Property<int>("Id").ValueGeneratedNever();
e.HasKey("Id");
e.Property<string>("Name").HasColumnType("json");

@AndriySvyryd AndriySvyryd Jun 19, 2026

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Also declare an index on this property to make sure it's recreated correctly

});
},
new AlterColumnOperation
{
Table = "Entity",
Name = "Name",
ClrType = typeof(string),
ColumnType = "nvarchar(max)",
IsNullable = true,
OldColumn = new AddColumnOperation
{
ClrType = typeof(string),
ColumnType = "json",
IsNullable = true
}
},
model =>
{
var table = Assert.Single(model.Tables);
var column = Assert.Single(table.Columns, c => c.Name == "Name");
Assert.Equal("nvarchar(max)", column.StoreType);
Assert.True(column.IsNullable);
});

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(max) NULL;
EXEC(N'UPDATE [Entity] SET [Name] = CONVERT(nvarchar(max), [ef_temp_Name])');
ALTER TABLE [Entity] DROP COLUMN [ef_temp_Name];
""");
}

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