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Automatically Generated Columns

The treelist allows you to automatically generate a column for each public property of its model rather than defining each column manually.

To enable Automatic Column Generation, set the AutoGenerateColumns parameter of the treelist to true.

The content of this article will be separated into groups for clarity:

Basics

To display all model fields in the treelist, just set its AutoGenerateColumns parameter to true.

If you don't need explicitly declared columns (such as a command column or frozen columns) the TreeListColumns tag is not required.

The auto-generated columns are not Expandable and the treelist will look like a grid. See the Customization section below to see how to set up at least one expandable column.

Use the AutoGenerateColumns parameter to generate columns out of a model

@* Data display requires only a single parameter. See the next examples for customizations and defining an expandable column to showcase hierarchy *@

<TelerikTreeList Data="@Data" AutoGenerateColumns="true"
                 Pageable="true" IdField="Id" ParentIdField="ParentId" Width="650px" Height="400px">
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample models and data generation

    public class Employee
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Name { get; set; }
        public DateTime HireDate { get; set; }
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null,
                Name = $"root: {i}",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

The result from the code snippet above.

screenshot of autogenerated columns only

Declare Explicit Columns

The treelist can consist of both Automatically Generated and explicitly declared columns.

The following examples show how you can control their order and positions:

Default Column Order

By default the Automatically Generated Columns are rendered after the manually declared ones.

Observe the default positioning of the Automatically Generated Columns

@* The autogenerated columns are after those you define manually. *@

<TelerikTreeList Data="@Data" AutoGenerateColumns="true"
                 Pageable="true" IdField="Id" ParentIdField="ParentId" Width="650px" Height="400px">
    <TreeListColumns>
        <TreeListCheckboxColumn />
    </TreeListColumns>
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample models and data generation

    public class Employee
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Name { get; set; }
        public DateTime HireDate { get; set; }
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null,
                Name = $"root: {i}",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

The result from the code snippet above

screenshot of autogenerated columns and checkbox column

Define Explicit Column Order

To set explicit position of the Automatically Generated Columns you can use the TreeListAutoGeneratedColumns tag inside the TreeListColumns tag and place it in the order you want it to have in relation to the columns you declare.

When the TreeListAutoGeneratedColumns tag is used the AutoGenerateColumns parameter of the treelist must also set to true.

Observe explicitly set position of the Automatically Generated Columns between a Checkbox and Command columns

@* For brevity, editing is not implemented in this example *@

<TelerikTreeList Data="@Data" AutoGenerateColumns="true"
                 Pageable="true" IdField="Id" ParentIdField="ParentId" Width="650px" Height="400px">
    <TreeListColumns>
        <TreeListCheckboxColumn />

        <TreeListAutoGeneratedColumns />

        <TreeListCommandColumn>
            <TreeListCommandButton Command="Edit">Edit</TreeListCommandButton>
        </TreeListCommandColumn>
    </TreeListColumns>
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample models and data generation

    public class Employee
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        public string Name { get; set; }
        public DateTime HireDate { get; set; }
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null,
                Name = $"root: {i}",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

The result from the code snippet above

screenshot of autogenerated columns and checkbox column

Customization

You can use data annotation attributes to control the column generation, in addition to the options explained above:

  • You can set the Title of the column through the [Display(Name="The Desired Title")] attribute on the fields of your model.

  • You can set the [Display(AutoGenerateField=false)] attribute over a property of your model if you want to prevent auto-generation of a column from that field.

  • You can prevent data mutation by setting the [Editable] attribute to false on fields of your model.

    • The properties that do not have a setter or the setter is not accessible (private) will not be editable either.
  • You can set custom width to all auto-generated columns through the ColumnWidth parameter of TreeListAutoGeneratedColumns. By default they will be equally distributed to fill the width of the treelist.

    • To enable horizontal scrolling, the ColumnWidth parameter has to be set so that the sum of all columns is greater than the treelist width. You can find more information in the Column Width article.

To use the attributes listed above the System.ComponentModel.DataAnnotations using statement has to be present in the file with your model. With Popup editing, you can use validation attributes in addition to the customization attributes.

Example

This example shows how to:

  • Define an expandable column to showcase hierarchy (define it explicitly, and skip it from column generation through the [Display(AutoGenerateField = false)] attribute).
  • Use data annotation attributes to
    • set the column titles (e.g., Email)
    • make a field non-editable (e.g., Id)
    • hide a field from the treelist (e.g., ParentId)
    • validate the data (e.g., Name)
  • Use the [Display(AutoGenerateField = false)] attribute to prevent a column from being generated, so you can declare it yourself and customize it (e.g., Name)
  • Select the order of the columns and set explicit position of the autogenerated Columns
  • Make CUD operations (only basic Editing is implemented here for brevity)

Observe the behavior of auto-generated columns with some customizations.

@using System.ComponentModel.DataAnnotations

<TelerikTreeList Data="@Data" AutoGenerateColumns="true"
                 Pageable="true" EditMode="@TreeListEditMode.Popup" OnUpdate="@UpdateHandler"
                 IdField="Id" ParentIdField="ParentId" Width="750px" Height="700px">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListAutoGeneratedColumns />
        <TreeListCommandColumn>
            <TreeListCommandButton Command="Edit">Edit</TreeListCommandButton>
        </TreeListCommandColumn>
    </TreeListColumns>
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    // sample models with annotations

    public class Employee
    {
        [Editable(false)] // non-editable autogenerated column
        public int Id { get; set; }

        [Display(AutoGenerateField = false)] // column will not be generated
        public int? ParentId { get; set; }

        [Display(AutoGenerateField = false)]
        [Required(ErrorMessage = "Name is a mandatory field for an employee")] // validation
        public string Name { get; set; }

        [Required(ErrorMessage = "Email address is mandatory field")]
        [EmailAddress(ErrorMessage = "Invalid Email Address")]
        [Display(Name = "Email")] // custom title for autogenerated column
        public string EmailAddress { get; set; }

        [Display(Name = "Hire Date")]
        public DateTime HireDate { get; set; }

        // Used for the editing so replacing the object in the view-model data
        // will treat it as the same object and keep its state - otherwise it will
        // collapse after editing is done, which is not what the user would expect
        public override bool Equals(object obj)
        {
            if (obj is Employee)
            {
                return this.Id == (obj as Employee).Id;
            }
            return false;
        }
    }

    // basic Update operation, the rest is not implemented for brevity

    async Task UpdateHandler(TreeListCommandEventArgs e)
    {
        var item = e.Item as Employee;

        // perform actual data source operations here through your service
        await MyService.Update(item);

        // update the local view-model data with the service data
        await GetTreeListData();
    }

    // data generation

    async Task GetTreeListData()
    {
        Data = await MyService.Read();
    }

    protected override async Task OnInitializedAsync()
    {
        await GetTreeListData();
    }

    // the following static class mimics an actual data service that handles the actual data source
    // replace it with your actual service through the DI, this only mimics how the API can look like and works for this standalone page
    public static class MyService
    {
        private static List<Employee> _data { get; set; } = new List<Employee>();

        public static async Task<List<Employee>> Read()
        {
            if (_data.Count < 1)
            {
                for (int i = 1; i < 15; i++)
                {
                    _data.Add(new Employee
                    {
                        Id = i,
                        ParentId = null,
                        Name = $"root: {i}",
                        HireDate = DateTime.Now.AddYears(-i)
                    }); ;

                    for (int j = 1; j < 4; j++)
                    {
                        int currId = i * 100 + j;
                        _data.Add(new Employee
                        {
                            Id = currId,
                            ParentId = i,
                            Name = $"first level child {j} of {i}",
                            HireDate = DateTime.Now.AddDays(-currId)
                        });

                        for (int k = 1; k < 3; k++)
                        {
                            int nestedId = currId * 1000 + k;
                            _data.Add(new Employee
                            {
                                Id = nestedId,
                                ParentId = currId,
                                Name = $"second level child {k} of {i} and {currId}",
                                HireDate = DateTime.Now.AddMinutes(-nestedId)
                            }); ;
                        }
                    }
                }
            }

            return await Task.FromResult(_data);
        }

        public static async Task Update(Employee itemToUpdate)
        {
            var index = _data.FindIndex(i => i.Id == itemToUpdate.Id);
            if (index != -1)
            {
                _data[index] = itemToUpdate;
            }
        }
    }
}

The result from the code snippet above

gif of auto-generated columns with CRUD, selection and Paging

See also

In this article
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