Supported, features, limitations and use in objects with aggregation, usage examples

Below are the main opportunities provided by LINQProvider.

In the examples ds is the service data obtained in the following way:

var ds = (SQLDataService)DataServiceProvider.DataService; 

Supported

Number

In addition to numerical attributes of the object in query is allowed to use constants, variables, and functions from them. All this will be calculated. For example, the query issuing all objects with the attribute Length set attribute Width 10:

int Number1 = 8;
int Number2 = 2;
IQueryable<Кошка> queryList = ds.Query<Кошка>();
IQueryable<Кошка> query = from pn in queryList where pn.Длина == Number1 + Number2 + pn.Ширина select pn;
List<DataObject> data = query.Cast<DataObject>().ToList();

It supports not only integer when building restrictions.

float length = 10.0f;
IQueryable<Улица> queryList = ds.Query<Улица>();
IQueryable<Улица> query = from pn in queryList where pn.Протяженность > length select pn;
List<DataObject> data = query.Cast<DataObject>().ToList();

Line

Contains, StartsWith, EndsWith

To work with strings Linq provider allows you to use the Contains methods as well as options of StartsWith, EndsWith a single operator. The use of other options StartsWith and EndsWith will throw an exception MethodSignatureException.

Choose cats whose names contain the string “Osh”

List<Кошка> cat = ds.Query<Кошка>(Кошка.Views.КошкаE).Where(o => o.Кличка.Contains("Osh")).ToList();

Regex

In LINQProvider is the minimum support Regex (the main restrictions are related to the fact that the pattern for the regular expression translates into a pattern search for design like in sql).

List<Порода> objss = ds.Query<Порода>(Порода.Views.ПородаE).Where(x => Regex.IsMatch(x.Название, "12.*3")).ToList();

Acceptable for use in regular expressions design: “.”, “.*”, “^”, “$”.

Date/Time

The restrictions on dates you can use various properties DateTime.

Linq provider does not provide a method DateTime.AddDays. When you try to use exception will be thrown NotImplementedException.

You can use the numeric date components such as year, month, day in month, hour, minute, day of the week. The days of the week are converted to numbers as in C# in the enumeration DayOfWeek (0 – Sunday, 1 – Monday .. 6 – Saturday). For this were added the function DayOfWeekZeroBased in addition to the old DayOfWeek.

When you try to use the properties of Ticks, Second, Millisecond, DayOfYear exception will be thrown MethodSignatureException.

Select fractures which were earlier than today:

List<Перелом> objss = ds.Query<Перелом>(Перелом.Views.ПереломE).Where(o => o.Дата.Date < DateTime.Now.Date).ToList();

To Apply AddYears

DateTime now = DateTime.Now;
List<Перелом> objss = ds.Query<Перелом>(Перелом.Views.ПереломE).Where(o => o.Дата.AddYears(1) < now.Date).ToList();

Select the fractures that occurred on Sunday.

List<Перелом> objss = ds.Query<Перелом>(Перелом.Views.ПереломE).Where(o => o.Дата.DayOfWeek == DayOfWeek.Sunday).ToList();

NullableDateTime

To make the comparison with NullableDateTime DateTime you need to bring them to the same type out Linq query.

DateTime date = new DateTime(2012, 1, 1);
NullableDateTime nullableDate = new NullableDateTime { Value = date };
// Datawedge is of type NullableDateTime. 
List<Кредит> objss = ds.Query<Кредит>(Кредит.Views.КредитE).Where(к => к.ДатаВыдачи < nullableDate).ToList();

Boolean

It is possible to use not only expressions, but also their combinations with the operations of the algebra of logic, as well as the use of constants true and false.

an Enumeration (enum)

Restriction on transfer rekomendovano to impose the following:

// First cache the enum value in a variable, then limit 
var типПерелома = ТипПерелома.Открытый;
ds.Query<Перелом>(Перелом.Views.ПереломE).Where(o => o.Тип == типПерелома).ToList();

General capabilities and features

Comparison with null

When comparing with null is available not only test for equality and inequality but also job operations “>”, “>=”, “<”, “<=”.

As in standard work with Linq, the expression of the “Property > null” where Property, for example, of the type int will return false.

ds.Query<Лапа>(Лапа.Views.ЛапаE).Where(x => x.РазмерNullableInt > null);

the performance of simple arithmetic operations

Inside Linq expressions can perform simple arithmetic operations:

string prefix = "prefix";
string postfix = "postfix";
ds.Query<Кошка>(Кошка.Views.КошкаE).Where(x => x.Кличка == prefix + postfix);

Restrictions LINQProvider

Among the major constraints can be specified as “projection” (the projection from the current sample, i.e. the descendants of the DataObject of some other type) and specification of constraints using grouping (Group By).

To use projection or groups should:

  • To obtain a collection of data objects for which you want grouping or projection, use LINQProvider.
  • Make an additional request to the collection using LINQ to Objects.

Work with the masters/detaylari/pseudocatalase

Keys (PrimaryKey):

To compare objects key you must use the method Equals:

ds.Query<Кошка>(Кошка.Views.КошкаE).Where(o => o.__PrimaryKey.Equals(кошка.__PrimaryKey));

Masters

There is a possibility to impose restrictions on the master, or his attributes of type int, long, bool, string, DateTime. For example:

Порода порода = ds.Query<Порода>(Порода.Views.ПородаE).First(); // Some object type breed 
Кошка кошка = ds.Query<Кошка>(Кошка.Views.КошкаE).FirstOrDefault(o => o.Порода == порода); //Get the first cat of this breed 
Кошка кошка2 = ds.Query<Кошка>(Кошка.Views.КошкаE).FirstOrDefault(o => o.Порода.Название == Wild); // Get the cat name breed 

In this case, allowed restrictions only to the masters of the first level. When you try to execute following code will throw an exception MasterLevelException.

Кошка кошка = ds.Query<Кошка>(Кошка.Views.КошкаE).FirstOrDefault(o => o.Порода.ТипПороды == порода.ТипПороды); //Using the wizard, the wizard will throw an exception 

But it is possible to impose restrictions on the masters of the n-th level by its PrimaryKey:

ds.Query<Кошка>(Кошка.Views.КошкаE).Where(o => ПородаPKs.Contains(o.Порода.ТипПороды.__PrimaryKey));

Detaily

Considering the features of writing Linq queries to arrays of datalow:

ds.Query<Порода>(Порода.Views.КотенокE).Where(
                x => x.Кошка.Лапа.Cast<Лапа>().Any(o => o.ТипЛапы.Название == "front")).ToList();

Pseudometal

Working with pseudocatalase described in the article Pseudometal in LinqProvider.

Examples of usage

  • Simple proofreading all entries:
var credits = ds.Query<Кредит>(Кредит.Views.КредитL.Name);
  • The imposition of constraints on a string field:
var личности = ds.Query<Личность>(Личность.Views.ЧеловекL.Name).Where(l => l.Фамилия == Petrov);
  • Imposition of limitations on the date:
var личности = ds.Query<Личность>(Личность.Views.ЧеловекL.Name).Where(l => l.ДатаРождения > new DateTime(1980, 1, 1));
  • The imposition of constraints on Boolean type:
var личности = ds.Query<Личность>(Личность.Views.ЧеловекL.Name).Where(l => l.Уволен);
  • Of course, terms can be combined:
var личности = ds.Query<Личность>(Личность.Views.ЧеловекL.Name).Where(l => l.Уволен && l.ДатаУвольнения > new DateTime(2012, 1, 1));
  • Imposition of limitations on the master (key):
var кредиты = ds.Query<Кредит>(Кредит.Views.КредитL.Name).Where(k => k.Клиент == klient);
  • Imposition of limitations on detali:
ds.Query<Порода>(Порода.Views.КотенокE).Where(x => x.Кошка.Лапа.Cast<Лапа>().Any(o => o.ТипЛапы.Название == "front")).ToList();
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