groceries/Groceries/Transactions/TransactionPromotionForm.razor

@using Groceries.Data
@using Microsoft.EntityFrameworkCore

@inject IDbContextFactory<AppDbContext> DbContextFactory

<form method="post" @attributes="AdditionalAttributes">
    <div class="form-field">
        <label class="form-field__label" for="transactionPromotionName">Name</label>
        <div class="form-field__control input">
            <input class="input__control" id="transactionPromotionName" name="name" value="@Promotion?.Name" required autofocus />
        </div>
    </div>

    <div class="form-field">
        <label class="form-field__label" for="transactionPromotionAmount">Amount</label>
        <div class="form-field__control input">
            @*<span class="input__inset">@CultureInfo.CurrentCulture.NumberFormat.CurrencySymbol</span>*@
            <input class="input__control" id="transactionPromotionAmount" name="amount" value="@Promotion?.Amount" type="number" min="0" step="0.01" required />
        </div>
    </div>

    <div class="form-field">
        <label class="form-field__label" for="transactionPromotionItemIds">
            Items <span class="form-field__corner-hint">Optional</span>
        </label>
        <select class="form-field__control select" id="transactionPromotionItemIds" name="itemIds" multiple>
            @foreach (var item in Transaction.Items)
            {
                <option value="@item.ItemId" selected="@selectedItemIds.Contains(item.ItemId)">
                    @itemNames.GetValueOrDefault(item.ItemId)
                </option>
            }
        </select>
    </div>

    @ChildContent
</form>

@code {
    [Parameter]
    public required Transaction Transaction { get; set; }

    [Parameter]
    public TransactionPromotion? Promotion { get; set; }

    [Parameter]
    public RenderFragment? ChildContent { get; set; }

    [Parameter(CaptureUnmatchedValues = true)]
    public Dictionary<string, object>? AdditionalAttributes { get; set; }

    private Guid[] selectedItemIds = [];
    private Dictionary<Guid, string> itemNames = new();

    protected override async Task OnParametersSetAsync()
    {
        selectedItemIds = Promotion?.Items.Select(item => item.Id).ToArray() ?? [];

        using var dbContext = DbContextFactory.CreateDbContext();
        var itemIds = Transaction.Items.Select(item => item.ItemId);
        itemNames = await dbContext.Items
            .Where(item => itemIds.Contains(item.Id))
            .ToDictionaryAsync(item => item.Id, item => string.Concat(item.Brand, " ", item.Name));
    }
}