DxGrid.CustomValidators Property

Allows you to declare custom validator components.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v24.2.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
public RenderFragment CustomValidators { get; set; }

Property Value

Type	Description
RenderFragment	A template (render fragment) that allows you to declare custom validators.

Remarks

The Grid uses the DataAnnotationsValidator to validate user input based on data annotation attributes defined in an edit model.

You can also create custom validator components as described in the following Microsoft topic: Validator components. To enable custom validation in the Grid, declare validator components in the CustomValidators template.

Note that the declared custom validators override the standard DataAnnotationsValidator. If you need to use DataAnnotationsValidator in addition to the custom validators, declare it in the CustomValidators template explicitly.

For more information about validation in the Grid, refer to the following topic: Validate User Input.

The following code snippet uses the custom validator to check the Title field value.

View Example: Custom Validation View Example: Display an error message from the Web API Service

Index.razor

@page "/"

@using CustomValidation.Models
@using Microsoft.EntityFrameworkCore
@inject IDbContextFactory<NorthwindContext> NorthwindContextFactory
@implements IDisposable

<DxGrid Data="GridDataSource"
        EditModelSaving="OnEditModelSaving"
        CustomizeDataRowEditor="OnCustomizeDataRowEditor"
        CustomizeEditModel="OnCustomizeEditModel"
        KeyFieldName="EmployeeId">
    <Columns>
        <DxGridCommandColumn DeleteButtonVisible="false" />
        <DxGridDataColumn FieldName="FirstName" />
        <DxGridDataColumn FieldName="LastName" />
        <DxGridDataColumn FieldName="Title" />
        <DxGridDataColumn FieldName="HireDate" />
    </Columns>
    <EditFormTemplate Context="editFormContext">
        <DxFormLayout>
            <DxFormLayoutItem Caption="First Name:">
                @editFormContext.GetEditor("FirstName")
            </DxFormLayoutItem>
            <DxFormLayoutItem Caption="Last Name:">
                @editFormContext.GetEditor("LastName")
            </DxFormLayoutItem>
            <DxFormLayoutItem Caption="Title:">
                @editFormContext.GetEditor("Title")
            </DxFormLayoutItem>
            <DxFormLayoutItem Caption="Hire Date:">
                @editFormContext.GetEditor("HireDate")
            </DxFormLayoutItem>
        </DxFormLayout>
    </EditFormTemplate>
    <CustomValidators>
        <MyCustomValidator DataItemValidating="ValidateGridData" />
    </CustomValidators>
</DxGrid>

@code {
    IEnumerable<object> GridDataSource { get; set; }
    NorthwindContext Northwind { get; set; }

    void ValidateGridData(ValidationMessageStoreEventArgs e) {
        var employee = (Employee)e.EditModel;
        if (employee.Title == null || !employee.Title.Contains("Sales")) {
            e.AddError(nameof(employee.Title), "The Title field value should contain 'Sales'.");
        }
    }

    protected override async Task OnInitializedAsync() {
        Northwind = NorthwindContextFactory.CreateDbContext();
        GridDataSource = await Northwind.Employees.ToListAsync();
    }

    void OnCustomizeEditModel(GridCustomizeEditModelEventArgs e) {
        if(e.IsNew) {
            var editModel = (Employee)e.EditModel;
            editModel.EmployeeId = GridDataSource.Count() + 1;
        }
    }

    async Task OnEditModelSaving(GridEditModelSavingEventArgs e) {
        var editModel = (Employee)e.EditModel;
        if (e.IsNew)
            await Northwind.AddAsync(editModel);
        else
            e.CopyChangesToDataItem();
        await Northwind.SaveChangesAsync();
        GridDataSource = await Northwind.Employees.ToListAsync();
    }

    void OnCustomizeDataRowEditor(GridCustomizeDataRowEditorEventArgs e) {
        if(e.EditSettings is ITextEditSettings settings)
            settings.ShowValidationIcon = true;
    }

    public void Dispose() {
        Northwind?.Dispose();
    }
}

CustomValidator.cs

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Forms;

namespace CustomValidation.Pages {
    public class ValidationMessageStoreEventArgs : EventArgs {
        public ValidationMessageStoreEventArgs(object model, Dictionary<string, List<string>> errors) {
            EditModel = model;
            Errors = errors;
        }
        public object EditModel { get; }
        private Dictionary<string, List<string>> Errors { get; }
        public void AddError(string fieldName, string errorText) {
            if (string.IsNullOrEmpty(fieldName) || string.IsNullOrEmpty(errorText))
                return;
            if (!Errors.ContainsKey(fieldName))
                Errors[fieldName] = new List<string>();
            Errors[fieldName].Add(errorText);
        }
    }
    public class MyCustomValidator : ComponentBase {
        private ValidationMessageStore MessageStore;
        [CascadingParameter]
        private EditContext CurrentEditContext { get; set; }
        [Parameter]
        public Action<ValidationMessageStoreEventArgs> DataItemValidating { get; set; }
        protected override void OnInitialized() {
            if (CurrentEditContext == null) {
                throw new InvalidOperationException(
                    $"{nameof(MyCustomValidator)} requires a cascading " +
                    $"parameter of type {nameof(EditContext)}. " +
                    $"For example, you can use {nameof(MyCustomValidator)} " +
                    $"inside an {nameof(EditForm)}.");
            }
            MessageStore = new(CurrentEditContext);
            CurrentEditContext.OnValidationRequested += (s, e) => ValidateData();
            CurrentEditContext.OnFieldChanged += (s, e) => ValidateData();
        }
        void ValidateData() {
            if (DataItemValidating == null)
                return;
            var errors = new Dictionary<string, List<string>>();
            var args = new ValidationMessageStoreEventArgs(CurrentEditContext.Model, errors);
            DataItemValidating.Invoke(args);

            MessageStore.Clear();
            foreach (var error in errors)
                MessageStore.Add(CurrentEditContext.Field(error.Key), error.Value);
            CurrentEditContext.NotifyValidationStateChanged();
        }
    }
}

Employee.cs

using System;
using System.Collections.Generic;

namespace CustomValidation.Models;

public partial class Employee {
    public int EmployeeId { get; set; }
    public string LastName { get; set; } = null!;
    public string FirstName { get; set; } = null!;
    public string? Title { get; set; }
    public DateTime? HireDate { get; set; }

}

NorthwindContext.cs

using System;
using System.Collections.Generic;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;

namespace CustomValidation.Models;

public partial class NorthwindContext : DbContext {
    public NorthwindContext() {}

    public NorthwindContext(DbContextOptions<NorthwindContext> options) : base(options) {}

    public virtual DbSet<Employee> Employees { get; set; }
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder) {
        modelBuilder.HasAnnotation("Relational:Collation", "SQL_Latin1_General_CP1_CI_AS");
        modelBuilder.Entity<Employee>(entity => {
            entity.HasIndex(e => e.EmployeeId, "EmployeeId");
            entity.HasIndex(e => e.LastName, "LastName");
            entity.HasIndex(e => e.FirstName, "FirstName");
            entity.HasIndex(e => e.Title, "Title");
            entity.HasIndex(e => e.HireDate, "HireDate");
        });
        OnModelCreatingPartial(modelBuilder);
    }
    partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
}

Program.cs

using Microsoft.EntityFrameworkCore;
// ...
builder.Services.AddDbContextFactory<NorthwindContext>((sp, options) => {
    var env = sp.GetRequiredService<IWebHostEnvironment>();
    var dbPath = Path.Combine(env.ContentRootPath, "Northwind.db");
    options.UseSqlite("Data Source=" + dbPath);
});

Implements

CustomValidators