Converting Filter and Sort Descriptors to SQL Queries in Blazor Grid
Environment
Product | Grid for Blazor |
Description
When using the Grid OnRead
event to execute SQL queries, I need to convert the Grid's filter and sort descriptors into SQL query statements. This way I can create SQL clauses for filtering and ordering items directly through SQL.
This KB article also answers the following questions:
- How can I convert Grid filters and sorters to SQL
WHERE
andORDER BY
clauses? - Is there a way to parse Grid filter and sort descriptors into SQL queries?
- Can I use
DataSourceRequest
to generate SQL query statements for filtering and sorting?
Solution
To convert the Grid's filter and sort descriptors into SQL query statements, you need to manually construct the SQL query within the OnRead
event handler by utilizing the args.Request.Filters
and args.Request.Sorts
objects. Although Telerik UI for Blazor does not provide a direct method to extract the SQL query from the DataSourceRequest
, you can achieve this manually.
The following steps outline how to achieve this:
- Add an
OnRead
event to your Grid and in the event handler, access theargs.Request.Filters
andargs.Request.Sorts
to construct your SQL query. - Iterate through
args.Request.Filters
to construct theWHERE
clause of your SQL query. Each filter in this collection will correspond to a column filter in the Grid. - Iterate through
args.Request.Sorts
to build theORDER BY
clause of your SQL query. Each sort descriptor corresponds to a column sorting in the Grid. - Form your complete SQL query and execute it against your database with the constructed
WHERE
andORDER BY
clauses. - Assign the result of your SQL query to the Grid by setting
args.Data
.
Example
Below is a simplified example demonstrating how to parse filter and sort descriptors. This example does not directly execute a SQL query but outlines how to construct the WHERE
and ORDER BY
clauses.
@using System.Text
@using Telerik.DataSource
@using Telerik.DataSource.Extensions
<TelerikGrid TItem="@MyItem"
OnRead="@ReadItems"
FilterMode="@GridFilterMode.FilterRow"
Sortable="true"
Pageable="true">
<GridColumns>
<GridColumn Field=@nameof(MyItem.ID) />
<GridColumn Field=@nameof(MyItem.Name) />
<GridColumn Field=@nameof(MyItem.Age) />
</GridColumns>
</TelerikGrid>
@code {
private List<MyItem> GridData { get; set; } = new();
private async Task ReadItems(GridReadEventArgs args)
{
string sqlQuery = string.Empty;
string filterQuery = BuildFilterQuery(args.Request.Filters);
string sortQuery = BuildSortQuery(args.Request.Sorts);
if (filterQuery != string.Empty)
{
sqlQuery = $"SELECT * FROM MyTable WHERE {filterQuery}";
GridData = await ExecuteSqlQuery(sqlQuery);
}
else if (sortQuery != string.Empty)
{
sqlQuery = $"SELECT * FROM MyTable ORDER BY {sortQuery}";
GridData = await ExecuteSqlQuery(sqlQuery);
}
else
{
GridData = GenerateData();
}
var datasourceResult = GridData.ToDataSourceResult(args.Request);
args.Data = datasourceResult.Data;
args.Total = datasourceResult.Total;
}
private string BuildFilterQuery(IEnumerable<IFilterDescriptor> filters)
{
// Implement logic to parse filters into SQL WHERE clause
// Example: "Name = 'John' AND Age > 30"
// You may need to adjust the SQL query depending if there are
// more FilterDescriptors (when using FilterMenu filter mode)
var filterQuery = new StringBuilder();
foreach (var filter in filters)
{
if (filter is CompositeFilterDescriptor compositeFilter)
{
foreach (var childFilter in compositeFilter.FilterDescriptors)
{
filterQuery.Append(ParseFilterDescriptor(childFilter));
}
}
}
return filterQuery.ToString();
}
private string ParseFilterDescriptor(IFilterDescriptor filter)
{
if (filter is FilterDescriptor descriptor)
{
return $"{descriptor.Member} {GetSqlOperator(descriptor.Operator)} '{descriptor.Value}'";
}
return string.Empty;
}
private string GetSqlOperator(FilterOperator filterOperator)
{
return filterOperator switch
{
FilterOperator.IsEqualTo => "=",
FilterOperator.IsNotEqualTo => "<>",
FilterOperator.IsGreaterThan => ">",
FilterOperator.IsGreaterThanOrEqualTo => ">=",
FilterOperator.IsLessThan => "<",
FilterOperator.IsLessThanOrEqualTo => "<=",
FilterOperator.Contains => "LIKE",
_ => throw new NotSupportedException($"Operator {filterOperator} is not supported")
};
}
private string BuildSortQuery(IEnumerable<SortDescriptor> sorts)
{
// Implement logic to parse sorters into SQL ORDER BY clause
// Example: "Name ASC"
return string.Join(", ", sorts.Select(s => $"{s.Member} {(s.SortDirection == ListSortDirection.Ascending ? "ASC" : "DESC")}"));
}
private async Task<List<MyItem>> ExecuteSqlQuery(string sqlQuery)
{
// Implement logic to execute the SQL query and return the result
// This is a placeholder for your actual data access code
//Remove this line when you execute the SQL query
//It is only for example purposes
GridData = new List<MyItem>();
return GridData;
}
protected override void OnInitialized()
{
GridData = GenerateData();
}
private List<MyItem> GenerateData()
{
var result = new List<MyItem>();
var rand = new Random();
for (int i = 0; i < 100; i++)
{
result.Add(new MyItem()
{
ID = i,
Name = "Name " + i,
Age = rand.Next(10, 40)
});
}
return result;
}
public class MyItem
{
public int ID { get; set; }
public string Name { get; set; }
public int Age { get; set; }
}
}