ISqlExecutor.SelectLazy<TModel>(ISqlQueryBuilder queryBuilder, params object[] parameters) Method

.NET Standard 2.x | Current Version (1.0.1)

0.5.0-alpha

1.0.1 (current)

Executes the SQL SELECT statement generated by an ISqlQueryBuilder object and returns an IEnumerable <TModel> object that can be used to load the result set lazily.

Namespace: SnapObjects.Data

Assembly: SnapObjects.Data.dll

Syntax

  public IEnumerable<TModel> SelectLazy<TModel>(ISqlQueryBuilder queryBuilder, params object[] parameters);

Type Parameters

TModel

The datatype of the model object which represents the data row in the result set.

You can also specify DynamicModel to TModel if you do not want to define a custom model class.

Parameters

queryBuilder SnapObjects.Data.ISqlQueryBuilder

A SqlQueryBuilder object which can be used to generate a SQL SELECT statement.

parameters System.Object[]

(Optional) One or more ParamValue objects which contain the values corresponding to the SQL parameter identifier names.

You can also pass the arguments directly in the order in which they appear in the SQL SELECT statement generated by queryBuilder without using the ParamValue object.

Returns

System.Collections.Generic.IEnumerable<TModel>

Returns an IEunmerable<TModel> object which can load the result set lazily.

Remarks

This method uses command behavior of System.Data.CommandBehavior.SequentialAccess internally, which provides a way for the DataReader to handle rows that contain columns with large binary values.

It creates each model object and reads data from database to this model object only when the data is asked for. You can use this method to save resources and improve performance by deferring the initialization of expensive objects until they are requested.

You have to open the current connection (DataContext.CurrentConnection property) explicitly before calling this method and close the connection explicitly after calling this method.

Examples

The following code example demonstrates how to use the SelectLazy<TModel>(ISqlQueryBuilder, params object[]) method to build and execute the SQL statement using SqlQueryBuilder and get the result set lazily.

using SnapObjects.Data;
using System;

namespace Appeon.ApiDoc.ISqlExecutorExamples
{
    public class SelectLazyExample
    {
        private readonly SchoolContext _context;

        public SelectLazyExample(SchoolContext dataContext)
        {
            // Sets the data context
            _context = dataContext;
        }

        public void Example2()
        {
            // Creates SqlQueryBuilder.
            var builder = new SqlQueryBuilder();

            // Defines the select list.
            string[] columns = { "CourseID", "Title" };

            // Defines the SQL statement.
            builder.Select(columns)
                    .From("Course")
                    .Where("CourseID", SqlBuilder.Parameter<int>("id"));

            // Opens the current connection.
            _context.CurrentConnection.Open();

            // Executes the SQL statement.
            // It dosen't get the result set from database.
            var result = _context.SqlExecutor.SelectLazy<DynamicModel>(builder, 2030);

            // Gets each row of the result set from database one by one. 
            // It creates each model object and reads data from database to 
            // this model object only when the data is asked for.
            // This method is usually used to handle rows that contain columns  
            // with large binary values.
            foreach (var model in result)
            {
                Console.WriteLine("Title: {0}.", model.GetValue(1));
            }

            // Closes the current connection.
            _context.CurrentConnection.Close();

            /*This code produces the following output:

            Title: Poetry.
            */
        }
    }
}

Applies to

.NET Standard

2.x