IQueryWhereBuilder.WhereExists(ISqlBuilder sqlBuilder) Method

.NET Standard 2.x

Creates a WHERE clause, and adds a search condition to the WHERE clause. Uses EXISTS to test for the existence of the record returned from a subquery.

Namespace: SnapObjects.Data

Assembly: SnapObjects.Data.dll

Syntax

IQueryAndOrBuilder<TModel> WhereExists(ISqlBuilder sqlBuilder);

Parameters

sqlBuilder SnapObjects.Data.ISqlBuilder

An ISqlBuilder object which represents a SQL subquery on the right of the EXISTS operator.

Returns

IQueryAndOrBuilder<TModel>

Returns an IQueryAndOrBuilder<TModel> object which can be used to add more search conditions to the current WHERE clause.

Examples

The following code example uses the WhereExists method to specify that the "DepartmentID" value of the "Department" table must exist in the result set of the subquery.

using Appeon.ApiDoc.Models.School;
using SnapObjects.Data;
using System;
using System.Threading.Tasks;

namespace Appeon.ApiDoc.IQueryWhereBuilderExamples
{
    public class WhereExistsExample
    {
        private SchoolContext _context;
        
        public WhereExistsExample(SchoolContext dataContext)
        {
            // Sets Data Context
            _context = dataContext;
        }

        public async Task<int> Example() 
        {
            // Get a QueryBuilder.
            var Builder = _context.SqlModelMapper.GetQueryBuilder<Department>();
            
            // Defines a subquery.
            var subsqlbuilder = new SqlQueryBuilder();
            subsqlbuilder.Select("1")
                .From("Department")
                .Where("departmentid", SqlBuilder.Parameter<int>("id"));
                
            // Specifies the WHERE EXIST condition:
            // the data exists in the result set of the subquery.
            Builder.WhereExists(subsqlbuilder);
            
            // Data with departmentID equal to 4 exists.
            var result = (await Builder.LoadAsync(4)).ToList();
            
            if (result.Count != 0)
            {
                // If the result of subquery is true, the data can be loaded.
                Console.WriteLine("The subquery result is true.");
            }
            else
            {
                // If the result of subquery is false, the data cannot be loaded.
                Console.WriteLine("The subquery result is false.");
            }
            
            return result.Count;
            
            /*This code example produces the following output:   
             
                The subquery result is true.
            */
        }
    }
}

Example Refer To

Model Class: Department

Applies to

.NET Standard

2.x