Added new kb article grid-convert-descriptors-to-sql

Author: KB Bot

knowledge-base/grid-convert-descriptors-to-sql.md

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+---
+title: Converting Filter and Sort Descriptors to SQL Queries in Blazor Grid
+description: Learn how to parse filter and sort descriptors from the Blazor Grid into SQL query statements for manual SQL queries execution using the OnRead event.
+type: how-to
+page_title: How to Parse Blazor Grid Descriptors into SQL Query Statements
+slug: grid-convert-descriptors-to-sql
+tags: grid, blazor, filter descriptors , sort descriptors, SQL query
+res_type: kb
+ticketid: 1666625, 1653361
+---
+
+## Environment
+
+<table>
+    <tbody>
+        <tr>
+            <td>Product</td>
+            <td>Grid for Blazor</td>
+        </tr>
+    </tbody>
+</table>
+
+## Description
+
+When using the Grid [`OnRead` event]({%slug grid-events%}#read-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 and ORDER BY clauses?
+- Is there a way to parse Grid filter and sort descriptors into SQL queries?
+- Can I use `DataSourceRequest`({%slug common-features-data-binding-onread%}#event-argument) 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`, a manual approach can be adopted. 
+
+The following steps outline how to achieve this:
+
+1. **Handle the `OnRead` Event**: Add an `OnRead` event to your Grid and in the event handler, access the `args.Request.Filters` and `args.Request.Sorts` to construct your SQL query.
+
+2. **Parse Filters**: Iterate through `args.Request.Filters` to construct the WHERE clause of your SQL query. Each filter in this collection will correspond to a column filter in the Grid.
+
+3. **Parse Sort Descriptors**: Similarly, iterate through `args.Request.Sorts` to build the ORDER BY clause of your SQL query. Each sort descriptor corresponds to a column sorting in the Grid.
+
+4. **Execute SQL Query**: With the constructed WHERE and ORDER BY clauses, form your complete SQL query and execute it against your database.
+
+5. **Set Grid Data**: Finally, 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.
+
+```csharp
+@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; }
+
+    private string SqlQuery { get; set; }
+    private string FilterQuery { get; set; }
+    private string SortQuery { get; set; }
+
+    private async Task ReadItems(GridReadEventArgs args)
+    {
+        FilterQuery = BuildFilterQuery(args.Request.Filters);
+        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
+        if (FilterQuery != string.Empty)
+        {
+        }
+
+        if (SortQuery != string.Empty)
+        {
+        }
+        //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; }
+    }
+}
+```
+
+## See Also
+
+- [OnRead Event Documentation]({%slug grid-events%}#read-event)
+- [Forum Post on Using DataSourceRequest in SQL Query](https://www.telerik.com/forums/can-datasourcerequest-be-used-in-sql-query-to-add-where-and-order-by-clauses)
+- [Get Information From the DataSourceRequest]({%slug components/grid/manual-operations%}#get-information-from-the-datasourcerequest)