Advanced for simple. data, advanced for simple. data
I. sorting results
-OrderBy (ascending)
-OrderByDescending (in descending order)
db.Product.All().OrderByFactoryName();db.Product.All().OrderByFactoryNameDescending();
Or
db.Product.All().OrderBy(db.Product.FactoryName);db.Product.All().OrderByDescending(db.Product.FactoryName);
Ii. Table join
1. No foreign key constraints
1.1 natural connections
-Join
-Left Join
-Outer Join
var q = _db.Order.Query().Join(_db.OrderDetail, ).Where(_db.OrderDetail.UnitPrice > 15000);List<dynamic> employees = q.Select(_db.Order.OrderCode, q.OrderDetail.CategoryName).ToList();
1.2 cascading Query
-
-WithOne
-WithMany
dynamic OrderDetailAlias;var OrderDetails = db.Order.All().With(db.Order.OrderDetail.As("OrderDetailInfo"), out OrderDetailAlias)
.Select( db.Order.OrderCode, BandAlias.Name);
2. Foreign key constraints
2.1. A single dataset is returned
var orders = _db.Order.FindAllByCustomerId(10).Select(_db.Order.OrderCode, q.Order.OrderDetail.CategoryName);
(Using the foreign key of the database)
var orders = _db.Order.FindAllByCustomerId(10).Select(_db.Order.OrderCode, _db.OrderDetail.CategoryName).Join(_db.OrderDetail).On(OrderId: _db.Order.PKID);
(Replace foreign key)
var orders = _db.Order.FindAllByCustomerId(10).Select(_db["Order"]["OrderCode"], _db["OrderDetail"]["CategoryName"]).Join(_db["OrderDetail"]).On(OrderId: _db["Order"]["PKID"]);
(Replace foreign key-index writing)
Iii. Aggregate functions
1. Having
var orderDetails= db.OrderDetail.All().Select(db.OrderDetail.Order.OrderCode, db.OrderDetail.PKID.Count().As("OrderDetailCount")).Having(db.OrderDetail.PKID.Count() > 2);
2. Max, Min, Sum, Count, and Avg
var orderDetails=db.OrderDetail.All().Having(db.OrderDetail.UnitPrice.Max()>100);
var orderDetails=db.OrderDetail.All().Having(db.OrderDetail.UnitPrice.Min()>100);
3. Count, CountDistinct
Var orderDetails = db. orderDetail. all (). select (db. orderDetail. orderId. count (); var orderDetails = db. orderDetail. all (). select (db. orderDetail. orderId. countDistinct (); deduplication count
Iv. Help Functions
1. Length (field Length)
var codeLength=db.Order.Select(db.Order.OrderCode.Length().As("CodeLength"));
2. Convert to Scalar Value
2.1. ToScalar and ToScalar <T> return an attribute as the scalar value from the query results.
int id=db.Order.Get(1).ToScalar();int id=db.Order.Select(db.Order.Id).Get(1).ToScalar();
2.2. ToScalarOrDefault and ToScalarOrDefault <T> return an attribute from the query result as the scalar value, which is the default value. If the attribute value is NULL, ToScalarOrDefault <T> Returns default <T>
string orderCode=db.Order.FindAllById(1).Select(db.Order.OrderCode).ToScalarOrDefault();
2.3. ToScalarList and ToScalarList <T> return a list from a series of query results as scalar values.
List<string> orderDetails=db.OrderDetail.FindAllByOrderId(1).Select(db.OrderDetail.CategoryName).ToScalarList<string>();
2.4. ToScalarArray and ToScalarArray <T> return an array as the scalar value from a series of query results.
string[] orderDetails=db.OrderDetail.FindAllByOrderId(1).Select(db.OrderDetail.CategoryName).ToScalarArray<string>();
To be continued...
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