diff --git a/DbFirst.API/Controllers/MassDataController.cs b/DbFirst.API/Controllers/MassDataController.cs
new file mode 100644
index 0000000..96d09f3
--- /dev/null
+++ b/DbFirst.API/Controllers/MassDataController.cs
@@ -0,0 +1,46 @@
+using DbFirst.Application.MassData;
+using DbFirst.Application.MassData.Commands;
+using DbFirst.Application.MassData.Queries;
+using MediatR;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DbFirst.API.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class MassDataController : ControllerBase
+{
+    private readonly IMediator _mediator;
+
+    public MassDataController(IMediator mediator)
+    {
+        _mediator = mediator;
+    }
+
+    [HttpGet]
+    public async Task<ActionResult<IEnumerable<MassDataReadDto>>> GetAll([FromQuery] int? skip, [FromQuery] int? take, CancellationToken cancellationToken)
+    {
+        var resolvedTake = take is null or <= 0 ? 200 : take;
+        var result = await _mediator.Send(new GetAllMassDataQuery(skip, resolvedTake), cancellationToken);
+        return Ok(result);
+    }
+
+    [HttpGet("{customerName}")]
+    public async Task<ActionResult<MassDataReadDto>> GetByCustomerName(string customerName, CancellationToken cancellationToken)
+    {
+        var result = await _mediator.Send(new GetMassDataByCustomerNameQuery(customerName), cancellationToken);
+        if (result == null)
+        {
+            return NotFound();
+        }
+
+        return Ok(result);
+    }
+
+    [HttpPost("upsert")]
+    public async Task<ActionResult<MassDataReadDto>> Upsert(MassDataWriteDto dto, CancellationToken cancellationToken)
+    {
+        var result = await _mediator.Send(new UpsertMassDataByCustomerNameCommand(dto), cancellationToken);
+        return Ok(result);
+    }
+}
diff --git a/DbFirst.API/Program.cs b/DbFirst.API/Program.cs
index 58e1536..98c6e0b 100644
--- a/DbFirst.API/Program.cs
+++ b/DbFirst.API/Program.cs
@@ -52,6 +52,7 @@ builder.Services.AddInfrastructure(builder.Configuration);
 builder.Services.AddApplication();
 
 builder.Services.AddScoped<ICatalogRepository, CatalogRepository>();
+builder.Services.AddScoped<IMassDataRepository, MassDataRepository>();
 
 builder.Services.AddDevExpressControls();
 builder.Services.AddSignalR();
diff --git a/DbFirst.API/appsettings.json b/DbFirst.API/appsettings.json
index d34692d..02a6d09 100644
--- a/DbFirst.API/appsettings.json
+++ b/DbFirst.API/appsettings.json
@@ -1,6 +1,7 @@
 {
   "ConnectionStrings": {
-    "DefaultConnection": "Server=SDD-VMP04-SQL17\\DD_DEVELOP01;Database=DD_ECM;User Id=sa;Password=dd;TrustServerCertificate=True;"
+    "DefaultConnection": "Server=SDD-VMP04-SQL17\\DD_DEVELOP01;Database=DD_ECM;User Id=sa;Password=dd;TrustServerCertificate=True;",
+    "MassDataConnection": "Server=SDD-VMP04-SQL19\\DD_DEVELOP01;Database=DD_ECM;User Id=sa;Password=dd;TrustServerCertificate=True;"
   },
   "Dashboard": {
     "BaseUrl": "https://localhost:7204"
diff --git a/DbFirst.Application/MassData/Commands/UpsertMassDataByCustomerNameCommand.cs b/DbFirst.Application/MassData/Commands/UpsertMassDataByCustomerNameCommand.cs
new file mode 100644
index 0000000..f719910
--- /dev/null
+++ b/DbFirst.Application/MassData/Commands/UpsertMassDataByCustomerNameCommand.cs
@@ -0,0 +1,5 @@
+using MediatR;
+
+namespace DbFirst.Application.MassData.Commands;
+
+public record UpsertMassDataByCustomerNameCommand(MassDataWriteDto Dto) : IRequest<MassDataReadDto>;
diff --git a/DbFirst.Application/MassData/Commands/UpsertMassDataByCustomerNameHandler.cs b/DbFirst.Application/MassData/Commands/UpsertMassDataByCustomerNameHandler.cs
new file mode 100644
index 0000000..e301fc9
--- /dev/null
+++ b/DbFirst.Application/MassData/Commands/UpsertMassDataByCustomerNameHandler.cs
@@ -0,0 +1,24 @@
+using AutoMapper;
+using DbFirst.Application.Repositories;
+using MediatR;
+
+namespace DbFirst.Application.MassData.Commands;
+
+public class UpsertMassDataByCustomerNameHandler : IRequestHandler<UpsertMassDataByCustomerNameCommand, MassDataReadDto>
+{
+    private readonly IMassDataRepository _repository;
+    private readonly IMapper _mapper;
+
+    public UpsertMassDataByCustomerNameHandler(IMassDataRepository repository, IMapper mapper)
+    {
+        _repository = repository;
+        _mapper = mapper;
+    }
+
+    public async Task<MassDataReadDto> Handle(UpsertMassDataByCustomerNameCommand request, CancellationToken cancellationToken)
+    {
+        var dto = request.Dto;
+        var updated = await _repository.UpsertByCustomerNameAsync(dto.CustomerName, dto.Amount, dto.StatusFlag, dto.Category, cancellationToken);
+        return _mapper.Map<MassDataReadDto>(updated);
+    }
+}
diff --git a/DbFirst.Application/MassData/MassDataProfile.cs b/DbFirst.Application/MassData/MassDataProfile.cs
new file mode 100644
index 0000000..b0f260c
--- /dev/null
+++ b/DbFirst.Application/MassData/MassDataProfile.cs
@@ -0,0 +1,12 @@
+using AutoMapper;
+using DbFirst.Domain.Entities;
+
+namespace DbFirst.Application.MassData;
+
+public class MassDataProfile : Profile
+{
+    public MassDataProfile()
+    {
+        CreateMap<Massdata, MassDataReadDto>();
+    }
+}
diff --git a/DbFirst.Application/MassData/MassDataReadDto.cs b/DbFirst.Application/MassData/MassDataReadDto.cs
new file mode 100644
index 0000000..db2fa09
--- /dev/null
+++ b/DbFirst.Application/MassData/MassDataReadDto.cs
@@ -0,0 +1,12 @@
+namespace DbFirst.Application.MassData;
+
+public class MassDataReadDto
+{
+    public int Id { get; set; }
+    public string CustomerName { get; set; } = string.Empty;
+    public decimal Amount { get; set; }
+    public string Category { get; set; } = string.Empty;
+    public bool StatusFlag { get; set; }
+    public DateTime AddedWhen { get; set; }
+    public DateTime? ChangedWhen { get; set; }
+}
diff --git a/DbFirst.Application/MassData/MassDataWriteDto.cs b/DbFirst.Application/MassData/MassDataWriteDto.cs
new file mode 100644
index 0000000..e1cacb5
--- /dev/null
+++ b/DbFirst.Application/MassData/MassDataWriteDto.cs
@@ -0,0 +1,9 @@
+namespace DbFirst.Application.MassData;
+
+public class MassDataWriteDto
+{
+    public string CustomerName { get; set; } = string.Empty;
+    public decimal Amount { get; set; }
+    public string Category { get; set; } = string.Empty;
+    public bool StatusFlag { get; set; }
+}
diff --git a/DbFirst.Application/MassData/Queries/GetAllMassDataHandler.cs b/DbFirst.Application/MassData/Queries/GetAllMassDataHandler.cs
new file mode 100644
index 0000000..e3003d0
--- /dev/null
+++ b/DbFirst.Application/MassData/Queries/GetAllMassDataHandler.cs
@@ -0,0 +1,23 @@
+using AutoMapper;
+using DbFirst.Application.Repositories;
+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public class GetAllMassDataHandler : IRequestHandler<GetAllMassDataQuery, List<MassDataReadDto>>
+{
+    private readonly IMassDataRepository _repository;
+    private readonly IMapper _mapper;
+
+    public GetAllMassDataHandler(IMassDataRepository repository, IMapper mapper)
+    {
+        _repository = repository;
+        _mapper = mapper;
+    }
+
+    public async Task<List<MassDataReadDto>> Handle(GetAllMassDataQuery request, CancellationToken cancellationToken)
+    {
+        var items = await _repository.GetAllAsync(request.Skip, request.Take, cancellationToken);
+        return _mapper.Map<List<MassDataReadDto>>(items);
+    }
+}
diff --git a/DbFirst.Application/MassData/Queries/GetAllMassDataQuery.cs b/DbFirst.Application/MassData/Queries/GetAllMassDataQuery.cs
new file mode 100644
index 0000000..84b350a
--- /dev/null
+++ b/DbFirst.Application/MassData/Queries/GetAllMassDataQuery.cs
@@ -0,0 +1,5 @@
+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public record GetAllMassDataQuery(int? Skip, int? Take) : IRequest<List<MassDataReadDto>>;
diff --git a/DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameHandler.cs b/DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameHandler.cs
new file mode 100644
index 0000000..7d518c9
--- /dev/null
+++ b/DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameHandler.cs
@@ -0,0 +1,23 @@
+using AutoMapper;
+using DbFirst.Application.Repositories;
+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public class GetMassDataByCustomerNameHandler : IRequestHandler<GetMassDataByCustomerNameQuery, MassDataReadDto?>
+{
+    private readonly IMassDataRepository _repository;
+    private readonly IMapper _mapper;
+
+    public GetMassDataByCustomerNameHandler(IMassDataRepository repository, IMapper mapper)
+    {
+        _repository = repository;
+        _mapper = mapper;
+    }
+
+    public async Task<MassDataReadDto?> Handle(GetMassDataByCustomerNameQuery request, CancellationToken cancellationToken)
+    {
+        var item = await _repository.GetByCustomerNameAsync(request.CustomerName, cancellationToken);
+        return item == null ? null : _mapper.Map<MassDataReadDto>(item);
+    }
+}
diff --git a/DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameQuery.cs b/DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameQuery.cs
new file mode 100644
index 0000000..26d75a6
--- /dev/null
+++ b/DbFirst.Application/MassData/Queries/GetMassDataByCustomerNameQuery.cs
@@ -0,0 +1,5 @@
+using MediatR;
+
+namespace DbFirst.Application.MassData.Queries;
+
+public record GetMassDataByCustomerNameQuery(string CustomerName) : IRequest<MassDataReadDto?>;
diff --git a/DbFirst.Application/Repositories/IMassDataRepository.cs b/DbFirst.Application/Repositories/IMassDataRepository.cs
new file mode 100644
index 0000000..b578dc9
--- /dev/null
+++ b/DbFirst.Application/Repositories/IMassDataRepository.cs
@@ -0,0 +1,10 @@
+using DbFirst.Domain.Entities;
+
+namespace DbFirst.Application.Repositories;
+
+public interface IMassDataRepository
+{
+    Task<List<Massdata>> GetAllAsync(int? skip = null, int? take = null, CancellationToken cancellationToken = default);
+    Task<Massdata?> GetByCustomerNameAsync(string customerName, CancellationToken cancellationToken = default);
+    Task<Massdata> UpsertByCustomerNameAsync(string customerName, decimal amount, bool statusFlag, string category, CancellationToken cancellationToken = default);
+}
diff --git a/DbFirst.Domain/Entities/Massdata.cs b/DbFirst.Domain/Entities/Massdata.cs
new file mode 100644
index 0000000..03b12e9
--- /dev/null
+++ b/DbFirst.Domain/Entities/Massdata.cs
@@ -0,0 +1,12 @@
+namespace DbFirst.Domain.Entities;
+
+public class Massdata
+{
+    public int Id { get; set; }
+    public string CustomerName { get; set; } = string.Empty;
+    public decimal Amount { get; set; }
+    public string Category { get; set; } = string.Empty;
+    public bool StatusFlag { get; set; }
+    public DateTime AddedWhen { get; set; }
+    public DateTime? ChangedWhen { get; set; }
+}
diff --git a/DbFirst.Infrastructure/DependencyInjection.cs b/DbFirst.Infrastructure/DependencyInjection.cs
index d01436f..4537270 100644
--- a/DbFirst.Infrastructure/DependencyInjection.cs
+++ b/DbFirst.Infrastructure/DependencyInjection.cs
@@ -11,6 +11,10 @@ public static class DependencyInjection
         services.Configure<TableConfigurations>(configuration.GetSection("TableConfigurations"));
         services.AddDbContext<ApplicationDbContext>(options =>
             options.UseSqlServer(configuration.GetConnectionString("DefaultConnection")));
+
+        services.AddDbContext<MassDataDbContext>(options =>
+            options.UseSqlServer(configuration.GetConnectionString("MassDataConnection")));
+
         return services;
     }
 }
diff --git a/DbFirst.Infrastructure/MassDataDbContext.cs b/DbFirst.Infrastructure/MassDataDbContext.cs
new file mode 100644
index 0000000..1975663
--- /dev/null
+++ b/DbFirst.Infrastructure/MassDataDbContext.cs
@@ -0,0 +1,44 @@
+using DbFirst.Domain.Entities;
+using Microsoft.EntityFrameworkCore;
+
+namespace DbFirst.Infrastructure;
+
+public class MassDataDbContext : DbContext
+{
+    public MassDataDbContext(DbContextOptions<MassDataDbContext> options)
+        : base(options)
+    {
+    }
+
+    public virtual DbSet<Massdata> Massdata { get; set; }
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.Entity<Massdata>(entity =>
+        {
+            entity.HasKey(e => e.Id);
+            entity.ToTable("MASSDATA");
+
+            entity.Property(e => e.Id).HasColumnName("ID");
+            entity.Property(e => e.CustomerName)
+                .HasMaxLength(200)
+                .IsUnicode(false)
+                .HasColumnName("CustomerName");
+            entity.Property(e => e.Amount)
+                .HasColumnType("decimal(12,2)")
+                .HasColumnName("Amount");
+            entity.Property(e => e.Category)
+                .HasMaxLength(100)
+                .IsUnicode(false)
+                .HasColumnName("Category");
+            entity.Property(e => e.StatusFlag)
+                .HasColumnName("StatusFlag");
+            entity.Property(e => e.AddedWhen)
+                .HasColumnType("datetime")
+                .HasColumnName("ADDED_WHEN");
+            entity.Property(e => e.ChangedWhen)
+                .HasColumnType("datetime")
+                .HasColumnName("CHANGED_WHEN");
+        });
+    }
+}
diff --git a/DbFirst.Infrastructure/Repositories/MassDataRepository.cs b/DbFirst.Infrastructure/Repositories/MassDataRepository.cs
new file mode 100644
index 0000000..e054a98
--- /dev/null
+++ b/DbFirst.Infrastructure/Repositories/MassDataRepository.cs
@@ -0,0 +1,66 @@
+using System.Data;
+using DbFirst.Application.Repositories;
+using DbFirst.Domain.Entities;
+using Microsoft.Data.SqlClient;
+using Microsoft.EntityFrameworkCore;
+
+namespace DbFirst.Infrastructure.Repositories;
+
+public class MassDataRepository : IMassDataRepository
+{
+    private readonly MassDataDbContext _db;
+
+    public MassDataRepository(MassDataDbContext db)
+    {
+        _db = db;
+    }
+
+    public async Task<List<Massdata>> GetAllAsync(CancellationToken cancellationToken = default)
+    {
+        return await _db.Massdata.AsNoTracking().ToListAsync(cancellationToken);
+    }
+
+    public async Task<Massdata?> GetByCustomerNameAsync(string customerName, CancellationToken cancellationToken = default)
+    {
+        return await _db.Massdata.AsNoTracking()
+            .FirstOrDefaultAsync(x => x.CustomerName == customerName, cancellationToken);
+    }
+
+    public async Task<List<Massdata>> GetAllAsync(int? skip = null, int? take = null, CancellationToken cancellationToken = default)
+    {
+        var query = _db.Massdata.AsNoTracking().OrderBy(x => x.Id).AsQueryable();
+
+        if (skip.HasValue)
+        {
+            query = query.Skip(skip.Value);
+        }
+
+        if (take.HasValue)
+        {
+            query = query.Take(take.Value);
+        }
+
+        return await query.ToListAsync(cancellationToken);
+    }
+
+    public async Task<Massdata> UpsertByCustomerNameAsync(string customerName, decimal amount, bool statusFlag, string category, CancellationToken cancellationToken = default)
+    {
+        var customerParam = new SqlParameter("@CustomerName", SqlDbType.VarChar, 200) { Value = customerName };
+        var amountParam = new SqlParameter("@Amount", SqlDbType.Decimal) { Value = amount, Precision = 12, Scale = 2 };
+        var statusParam = new SqlParameter("@StatusFlag", SqlDbType.Bit) { Value = statusFlag };
+        var categoryParam = new SqlParameter("@Category", SqlDbType.VarChar, 100) { Value = category };
+
+        await _db.Database.ExecuteSqlRawAsync(
+            "EXEC dbo.PRMassdata_UpsertByCustomerName @CustomerName, @Amount, @StatusFlag, @Category",
+            parameters: new[] { customerParam, amountParam, statusParam, categoryParam },
+            cancellationToken: cancellationToken);
+
+        var updated = await GetByCustomerNameAsync(customerName, cancellationToken);
+        if (updated == null)
+        {
+            throw new InvalidOperationException("Upsert completed but record could not be loaded.");
+        }
+
+        return updated;
+    }
+}