Reading and writing data

Reading and writing data#

Storing objects#

To store data to the database use DbContext.Add(object) as follows:

using Microsoft.EntityFrameworkCore;

var db = new InventorySystemDbContext();
db.Database.EnsureDeleted();
db.Database.EnsureCreated();

List<Item> items =
[
    new UnitItem
    {
        Id = "M3 screw",
        PricePerUnit = 1,
        InventoryLocation = 1,
        Quantity = 1000,
        Weight = 0.001m
    },
    new BulkItem
    {
        Id = "crank oil",
        PricePerUnit = 1.5m,
        InventoryLocation = 2,
        MeasurementUnit = "l",
        Quantity = 10
    }
];

List<Inventory> inventories =
[
    new()
    {
        Id = "wind turbine parts",
        Stock = items
    },
    new()
    {
        Id = "electronics",
        Stock = []
    }
];

foreach (var inventory in inventories)
    db.Add(inventory);
db.SaveChanges();

public class InventorySystemDbContext : DbContext
{
    public DbSet<Inventory> Inventories { get; set; }
    public DbSet<UnitItem> UnitItems { get; set; }
    public DbSet<BulkItem> BulkItems { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlite("Data Source=../../../inventory.sqlite");
    }
}

public class Item
{
    public string Id { get; set; }
    public decimal PricePerUnit { get; set; }
    public decimal Quantity { get; set; }
    public uint InventoryLocation { get; set; }
}

public class BulkItem : Item
{
    public string MeasurementUnit { get; set; }
}

public class UnitItem : Item
{
    public decimal Weight { get; set; }
}

public class Inventory
{
    public const decimal LowStockThreshold = 5;
    public string Id { get; set; }
    public List<Item> Stock { get; set; }
}

Now double click Item on the Database tool, to browse its contents. You will see:

Id

PricePerUnit

Quantity

InventoryLocation

Discriminator

InventoryId

MeasurementUnit

Weight

crank oil

1.5

10.0

2

BulkItem

wind turbine parts

l

null

M3 screw

1.0

1000.0

1

UnitItem

wind turbine parts

null

0.001

Tip

You can also add/modify/delete data using the Database tool in Rider.

Reading objects from a database#

Typically we have a database with data inside. Using inventory.sqlite with inventory data inside we can read data as follows:

using Microsoft.EntityFrameworkCore;

var db = new InventorySystemDbContext();
var inventories = db.Inventories.Include(inventory => inventory.Stock).ToList();
foreach (var inventory in inventories)
    if (inventory.Id == "wind turbine parts")
        Console.WriteLine(inventory.Stock.Count);

public class InventorySystemDbContext : DbContext
{
    public DbSet<Inventory> Inventories { get; set; }
    public DbSet<UnitItem> UnitItems { get; set; }
    public DbSet<BulkItem> BulkItems { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlite("Data Source=../../../inventory.sqlite");
    }
}

public class Item
{
    public string Id { get; set; }
    public decimal PricePerUnit { get; set; }
    public decimal Quantity { get; set; }
    public uint InventoryLocation { get; set; }
}

public class BulkItem : Item
{
    public string MeasurementUnit { get; set; }
}

public class UnitItem : Item
{
    public decimal Weight { get; set; }
}

public class Inventory
{
    public const decimal LowStockThreshold = 5;
    public string Id { get; set; }
    public List<Item> Stock { get; set; }
}

The code outputs the number of items in one of the inventories.

Explanation:

  • db.Inventories represents the inventories table in the database which maps to a list of Inventory objects

  • .Include(inventory => inventory.Stock) also initializes Stock property in the Inventory class.

    Without .Include, Stock property will be not initialized.

  • .ToList() creates a list of Inventory objects which we can process, e.g., with a foreach loop

Appendix#

Contents