Add soft-delete support to DataMerge

Author: pwelter34

src/FluentCommand.SqlServer/Merge/DataMerge.cs

@@ -50,6 +50,18 @@ public IDataMerge IncludeDelete(bool value = true)
         return this;
     }
 
+    /// <inheritdoc/>
+    public IDataMerge SoftDelete(string column, object? value = null)
+    {
+        if (string.IsNullOrWhiteSpace(column))
+            throw new ArgumentException("The soft delete column name is required.", nameof(column));
+
+        _mergeDefinition.SoftDeleteColumn = column;
+        _mergeDefinition.SoftDeleteValue = value ?? true;
+        _mergeDefinition.IncludeDelete = true;
+        return this;
+    }
+
     /// <inheritdoc/>
     public IDataMerge IdentityInsert(bool value = true)
     {

src/FluentCommand.SqlServer/Merge/DataMergeDefinition.cs

@@ -65,6 +65,27 @@ public DataMergeDefinition()
     /// </value>
     public bool IncludeDelete { get; set; }
 
+    /// <summary>
+    /// Gets or sets the name of the column in the <see cref="TargetTable"/> used to flag rows as soft deleted.
+    /// When <see cref="IncludeDelete"/> is <c>true</c> and this value is set, target rows not found in the source
+    /// are updated with <see cref="SoftDeleteValue"/> instead of being deleted.
+    /// </summary>
+    /// <value>
+    /// The soft delete column name, or <c>null</c> to use hard delete.
+    /// </value>
+    /// <remarks>
+    /// Soft deleted rows are reported with an <c>UPDATE</c> action in merge output.
+    /// </remarks>
+    public string? SoftDeleteColumn { get; set; }
+
+    /// <summary>
+    /// Gets or sets the value assigned to <see cref="SoftDeleteColumn"/> when a row is soft deleted.
+    /// </summary>
+    /// <value>
+    /// The soft delete value.
+    /// </value>
+    public object? SoftDeleteValue { get; set; }
+
     /// <summary>
     /// Gets or sets a value indicating whether to output the inserted, updated, or deleted values from the <see cref="TargetTable"/> after the merge operation.
     /// </summary>

src/FluentCommand.SqlServer/Merge/DataMergeGenerator.cs

@@ -379,6 +379,32 @@ private static void AppendDelete(DataMergeDefinition mergeDefinition, StringBuil
         if (!mergeDefinition.IncludeDelete)
             return;
 
+        if (mergeDefinition.SoftDeleteColumn.HasValue())
+        {
+            var column = QuoteIdentifier(mergeDefinition.SoftDeleteColumn!);
+            var value = mergeDefinition.SoftDeleteValue;
+            var literal = GetValue(value);
+
+            if (value != null && value != DBNull.Value && NeedQuote(value.GetType()))
+                literal = $"'{literal.Replace("'", "''")}'";
+
+            builder
+                .Append("WHEN NOT MATCHED BY SOURCE AND (t.")
+                .Append(column)
+                .Append(" IS NULL OR t.")
+                .Append(column)
+                .Append(" <> ")
+                .Append(literal)
+                .AppendLine(") THEN ")
+                .Append(' ', TabSize)
+                .Append("UPDATE SET t.")
+                .Append(column)
+                .Append(" = ")
+                .AppendLine(literal);
+
+            return;
+        }
+
         builder
             .AppendLine("WHEN NOT MATCHED BY SOURCE THEN ")
             .Append(' ', TabSize)

src/FluentCommand.SqlServer/Merge/IDataMerge.cs

@@ -28,6 +28,16 @@ public interface IDataMerge
     /// <returns>The same <see cref="IDataMerge"/> instance for fluent chaining.</returns>
     IDataMerge IncludeDelete(bool value = true);
 
+    /// <summary>
+    /// Specifies that target rows not found in the source data are soft deleted by setting <paramref name="column"/> to <paramref name="value"/>.
+    /// This also enables <see cref="IncludeDelete(bool)"/>.
+    /// </summary>
+    /// <param name="column">The target column used to flag rows as deleted.</param>
+    /// <param name="value">The value assigned to the column for soft deleted rows. Defaults to <c>true</c> when <c>null</c>.</param>
+    /// <returns>The same <see cref="IDataMerge"/> instance for fluent chaining.</returns>
+    /// <remarks>Soft deleted rows are reported with an <c>UPDATE</c> action in merge output.</remarks>
+    IDataMerge SoftDelete(string column, object? value = null);
+
     /// <summary>
     /// Specifies whether to allow identity insert on the target table during the merge operation.
     /// </summary>

test/FluentCommand.SqlServer.Tests/DataMergeGeneratorTests.cs

@@ -68,6 +68,60 @@ public void QuoteIdentifier()
 
     }
 
+    [Fact]
+    public void BuildMergeSoftDeleteBoolean()
+    {
+        var definition = DataMergeDefinition.Create<UserImport>();
+        definition.TargetTable = "dbo.User";
+        definition.IncludeDelete = true;
+        definition.SoftDeleteColumn = "IsDeleted";
+        definition.SoftDeleteValue = true;
+
+        var sql = DataMergeGenerator.BuildMerge(definition);
+
+        sql.Should().Contain("WHEN NOT MATCHED BY SOURCE AND (t.[IsDeleted] IS NULL OR t.[IsDeleted] <> 1) THEN \r\n    UPDATE SET t.[IsDeleted] = 1".ReplaceLineEndings());
+    }
+
+    [Fact]
+    public void BuildMergeSoftDeleteString()
+    {
+        var definition = DataMergeDefinition.Create<UserImport>();
+        definition.TargetTable = "dbo.User";
+        definition.IncludeDelete = true;
+        definition.SoftDeleteColumn = "Status";
+        definition.SoftDeleteValue = "O'Deleted";
+
+        var sql = DataMergeGenerator.BuildMerge(definition);
+
+        sql.Should().Contain("UPDATE SET t.[Status] = 'O''Deleted'");
+    }
+
+    [Fact]
+    public void BuildMergeHardDeleteWithoutSoftDeleteColumn()
+    {
+        var definition = DataMergeDefinition.Create<UserImport>();
+        definition.TargetTable = "dbo.User";
+        definition.IncludeDelete = true;
+
+        var sql = DataMergeGenerator.BuildMerge(definition);
+
+        sql.Should().Contain("WHEN NOT MATCHED BY SOURCE THEN \r\n    DELETE".ReplaceLineEndings());
+    }
+
+    [Fact]
+    public void BuildMergeNoDeleteWhenIncludeDeleteFalse()
+    {
+        var definition = DataMergeDefinition.Create<UserImport>();
+        definition.TargetTable = "dbo.User";
+        definition.IncludeDelete = false;
+        definition.SoftDeleteColumn = "IsDeleted";
+        definition.SoftDeleteValue = true;
+
+        var sql = DataMergeGenerator.BuildMerge(definition);
+
+        sql.Should().NotContain("NOT MATCHED BY SOURCE");
+    }
+
     [Fact]
     public async System.Threading.Tasks.Task BuildMergeTests()
     {