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Added new kb article grid-convert-descriptors-to-sql (#2434)
* Added new kb article grid-convert-descriptors-to-sql * update slug * Update knowledge-base/grid-convert-descriptors-to-sql.md Co-authored-by: Iva Stefanova Koevska-Atanasova <koevska@progress.com> * Update knowledge-base/grid-convert-descriptors-to-sql.md Co-authored-by: Iva Stefanova Koevska-Atanasova <koevska@progress.com> * update after review * Update knowledge-base/grid-convert-descriptors-to-sql.md Co-authored-by: Dimo Dimov <961014+dimodi@users.noreply.github.com> * update example --------- Co-authored-by: KB Bot <kb-bot@telerik.com> Co-authored-by: NansiYancheva <nansi.qncheva@abv.bg> Co-authored-by: NansiYancheva <106161782+NansiYancheva@users.noreply.github.com> Co-authored-by: Iva Stefanova Koevska-Atanasova <koevska@progress.com> Co-authored-by: Dimo Dimov <961014+dimodi@users.noreply.github.com>
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---
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title: Converting Filter and Sort Descriptors to SQL Queries in Blazor Grid
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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.
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type: how-to
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page_title: How to Parse Blazor Grid Descriptors into SQL Query Statements
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slug: grid-convert-descriptors-to-sql
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tags: grid, blazor, filter descriptors , sort descriptors, SQL query
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res_type: kb
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ticketid: 1666625, 1653361
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---
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## Environment
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<table>
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<tbody>
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<tr>
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<td>Product</td>
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<td>Grid for Blazor</td>
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</tr>
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</tbody>
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</table>
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## Description
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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.
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This KB article also answers the following questions:
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- How can I convert Grid filters and sorters to SQL `WHERE` and `ORDER BY` clauses?
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- Is there a way to parse Grid filter and sort descriptors into SQL queries?
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- Can I use [`DataSourceRequest`]({%slug common-features-data-binding-onread%}#event-argument) to generate SQL query statements for filtering and sorting?
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## Solution
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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.
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The following steps outline how to achieve this:
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1. 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.
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1. 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.
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1. 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.
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1. Form your complete SQL query and execute it against your database with the constructed `WHERE` and `ORDER BY` clauses.
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1. Assign the result of your SQL query to the Grid by setting `args.Data`.
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## Example
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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.
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```csharp
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@using System.Text
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@using Telerik.DataSource
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@using Telerik.DataSource.Extensions
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<TelerikGrid TItem="@MyItem"
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OnRead="@ReadItems"
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FilterMode="@GridFilterMode.FilterRow"
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Sortable="true"
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Pageable="true">
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<GridColumns>
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<GridColumn Field=@nameof(MyItem.ID) />
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<GridColumn Field=@nameof(MyItem.Name) />
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<GridColumn Field=@nameof(MyItem.Age) />
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</GridColumns>
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</TelerikGrid>
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@code {
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private List<MyItem> GridData { get; set; } = new();
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private async Task ReadItems(GridReadEventArgs args)
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{
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string sqlQuery = string.Empty;
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string filterQuery = BuildFilterQuery(args.Request.Filters);
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string sortQuery = BuildSortQuery(args.Request.Sorts);
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if (filterQuery != string.Empty)
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{
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sqlQuery = $"SELECT * FROM MyTable WHERE {filterQuery}";
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GridData = await ExecuteSqlQuery(sqlQuery);
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}
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else if (sortQuery != string.Empty)
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{
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sqlQuery = $"SELECT * FROM MyTable ORDER BY {sortQuery}";
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GridData = await ExecuteSqlQuery(sqlQuery);
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}
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else
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{
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GridData = GenerateData();
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}
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var datasourceResult = GridData.ToDataSourceResult(args.Request);
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args.Data = datasourceResult.Data;
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args.Total = datasourceResult.Total;
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}
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private string BuildFilterQuery(IEnumerable<IFilterDescriptor> filters)
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{
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// Implement logic to parse filters into SQL WHERE clause
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// Example: "Name = 'John' AND Age > 30"
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// You may need to adjust the SQL query depending if there are
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// more FilterDescriptors (when using FilterMenu filter mode)
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var filterQuery = new StringBuilder();
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foreach (var filter in filters)
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{
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if (filter is CompositeFilterDescriptor compositeFilter)
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{
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foreach (var childFilter in compositeFilter.FilterDescriptors)
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{
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filterQuery.Append(ParseFilterDescriptor(childFilter));
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}
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}
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}
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return filterQuery.ToString();
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}
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private string ParseFilterDescriptor(IFilterDescriptor filter)
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{
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if (filter is FilterDescriptor descriptor)
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{
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return $"{descriptor.Member} {GetSqlOperator(descriptor.Operator)} '{descriptor.Value}'";
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}
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return string.Empty;
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}
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private string GetSqlOperator(FilterOperator filterOperator)
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{
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return filterOperator switch
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{
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FilterOperator.IsEqualTo => "=",
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FilterOperator.IsNotEqualTo => "<>",
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FilterOperator.IsGreaterThan => ">",
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FilterOperator.IsGreaterThanOrEqualTo => ">=",
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FilterOperator.IsLessThan => "<",
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FilterOperator.IsLessThanOrEqualTo => "<=",
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FilterOperator.Contains => "LIKE",
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_ => throw new NotSupportedException($"Operator {filterOperator} is not supported")
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};
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}
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private string BuildSortQuery(IEnumerable<SortDescriptor> sorts)
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{
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// Implement logic to parse sorters into SQL ORDER BY clause
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// Example: "Name ASC"
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return string.Join(", ", sorts.Select(s => $"{s.Member} {(s.SortDirection == ListSortDirection.Ascending ? "ASC" : "DESC")}"));
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}
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private async Task<List<MyItem>> ExecuteSqlQuery(string sqlQuery)
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{
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// Implement logic to execute the SQL query and return the result
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// This is a placeholder for your actual data access code
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//Remove this line when you execute the SQL query
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//It is only for example purposes
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GridData = new List<MyItem>();
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return GridData;
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}
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protected override void OnInitialized()
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{
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GridData = GenerateData();
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}
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private List<MyItem> GenerateData()
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{
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var result = new List<MyItem>();
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var rand = new Random();
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for (int i = 0; i < 100; i++)
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{
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result.Add(new MyItem()
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{
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ID = i,
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Name = "Name " + i,
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Age = rand.Next(10, 40)
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});
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}
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return result;
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}
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public class MyItem
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{
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public int ID { get; set; }
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public string Name { get; set; }
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public int Age { get; set; }
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}
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}
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```
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## See Also
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- [OnRead Event Documentation]({%slug grid-events%}#read-event)
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- [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)
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- [Get Information From the DataSourceRequest]({%slug components/grid/manual-operations%}#get-information-from-the-datasourcerequest)
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