LLBL Gen Pro是一個為.NET開發人員設計的的對象關系映射(ORM)框架，與NHibernate,Entity Framework等框架一樣，通過實體與數據表的映射，實現關系數據庫持久化。
1 LLBL Gen Pro 入門 LLBL Gen Pro Basic
打開LLBL Gen Pro程序，在右邊的數據庫瀏覽器(Catelog Explorer)中根結點右鍵選擇從關系數據庫創建關系模型(
Add Relational Model Data from a Database)，然后根據SQL Server，並且填入登錄帳號和密碼。
最終的界面如下圖的所示，點擊工具欄按鈕生成.NET項目文件和實體映射文件。
1.1 持久化類 Persistent classes
以數據庫表銷售合同為例，它的數據庫表結構定義如下。
CREATE TABLE [dbo].[SLORDR] ( [RECNUM] [decimal] (18, 0) NOT NULL IDENTITY(1, 1), [CONTRACT_NO] [nvarchar] (20) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL, [CUSTOMER_NO] [nvarchar] (8) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, [CUSTOMER_NAME] [nvarchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, [CONTRACT_DATE] [datetime] NULL, [REMARK] [nvarchar] (4000) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, [CREATED_DATE] [datetime] NULL, [CREATED_BY] [nvarchar] (8) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, [REVISED_DATE] [datetime] NULL, [REVISED_BY] [nvarchar] (8) COLLATE SQL_Latin1_General_CP1_CI_AS NULL, [CLOSED] [nvarchar] (1) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ) ON [PRIMARY] GO ALTER TABLE [dbo].[SLORDR] ADD CONSTRAINT [PK_SLORDR] PRIMARY KEY CLUSTERED ([CONTRACT_NO]) ON [PRIMARY] GO
通過LLBL Gen Pro，生成的實體的代碼量比較多，上面的銷售合同數據表生成的實體類型定義源代碼有600多行。作為入門的例子，先了解LLBL Gen Pro生成的構造方法和字段映射。先看銷售合同實體的構造方法：
/// <summary> Static CTor for setting up custom property hashtables. Is executed before the first instance of this entity class or derived classes is constructed. </summary> static SalesContractEntity() { SetupCustomPropertyHashtables(); } /// <summary> CTor</summary> public SalesContractEntity():base("SalesContractEntity") { InitClassEmpty(null, null); } /// <summary> CTor</summary> /// <remarks>For framework usage.</remarks> /// <param name="fields">Fields object to set as the fields for this entity.</param> public SalesContractEntity(IEntityFields2 fields):base("SalesContractEntity") { InitClassEmpty(null, fields); } /// <summary> CTor</summary> /// <param name="validator">The custom validator object for this SalesContractEntity</param> public SalesContractEntity(IValidator validator):base("SalesContractEntity") { InitClassEmpty(validator, null); } /// <summary> CTor</summary> /// <param name="contractNo">PK value for SalesContract which data should be fetched into this SalesContract object</param> /// <remarks>The entity is not fetched by this constructor. Use a DataAccessAdapter for that.</remarks> public SalesContractEntity(System.String contractNo):base("SalesContractEntity") { InitClassEmpty(null, null); this.Fields[(int)SalesContractFieldIndex.ContractNo].CurrentValue = contractNo; } /// <summary> CTor</summary> /// <param name="contractNo">PK value for SalesContract which data should be fetched into this SalesContract object</param> /// <param name="validator">The custom validator object for this SalesContractEntity</param> /// <remarks>The entity is not fetched by this constructor. Use a DataAccessAdapter for that.</remarks> public SalesContractEntity(System.String contractNo, IValidator validator):base("SalesContractEntity") { InitClassEmpty(validator, null); this.Fields[(int)SalesContractFieldIndex.ContractNo].CurrentValue = contractNo; } /// <summary> Protected CTor for deserialization</summary> /// <param name="info"></param> /// <param name="context"></param> [EditorBrowsable(EditorBrowsableState.Never)] protected SalesContractEntity(SerializationInfo info, StreamingContext context) : base(info, context) { if(SerializationHelper.Optimization != SerializationOptimization.Fast) { _salesContractDetail = (EntityCollection<SalesContractDetailEntity>)info.GetValue("_salesContractDetail", typeof(EntityCollection<SalesContractDetailEntity>)); this.FixupDeserialization(FieldInfoProviderSingleton.GetInstance()); } // __LLBLGENPRO_USER_CODE_REGION_START DeserializationConstructor // __LLBLGENPRO_USER_CODE_REGION_END }
一共是7個構造方法，它們的作用說明如下：
1 靜態構造方法 調用SetupCustomPropertyHashtables方法以初始化屬性的自定義元數據。
2 默認無參數構造方法，以主鍵為參數的構造方法應用於實際開發過程。
3 以IEntityFields2為參數的構造方法，被框架使用。
4 以IValidator為參數的構造方法，用於自定義驗證類型。
5 以SerializationInfo為參數的方法用於序列化傳輸。
1.2 映射 Mapping
LLBL Gen Pro框架工具會生成2個項目文件，實體定義放在項目DatabaseGeneric中，實體與數據表的映射放在DatabaseSpecific，也就是前者是數據庫無關的，后者與數據庫的具體特性相關聯。比如生成存儲過程調用，則代碼生成會放到DatabaseSpecific項目中。來看一下上面的銷售合同表是如何與實體映射的。
/// <summary>Inits SalesContractEntity's mappings</summary> private void InitSalesContractEntityMappings() { this.AddElementMapping( "SalesContractEntity", "dbEnterprise", @"dbo", "SLORDR", 11 ); this.AddElementFieldMapping( "SalesContractEntity", "Recnum", "RECNUM", false, "Decimal", 0, 0, 18, true, "SCOPE_IDENTITY()", null, typeof(System.Decimal), 0 ); this.AddElementFieldMapping( "SalesContractEntity", "ContractNo", "CONTRACT_NO", false, "NVarChar", 20, 0, 0, false, "", null, typeof(System.String), 1 ); this.AddElementFieldMapping( "SalesContractEntity", "CustomerNo", "CUSTOMER_NO", true, "NVarChar", 8, 0, 0, false, "", null, typeof(System.String), 2 ); this.AddElementFieldMapping( "SalesContractEntity", "CustomerName", "CUSTOMER_NAME", true, "NVarChar", 50, 0, 0, false, "", null, typeof(System.String), 3 ); this.AddElementFieldMapping( "SalesContractEntity", "ContractDate", "CONTRACT_DATE", true, "DateTime", 0, 0, 0, false, "", null, typeof(System.DateTime), 4 ); this.AddElementFieldMapping( "SalesContractEntity", "Remark", "REMARK", true, "NVarChar", 4000, 0, 0, false, "", null, typeof(System.String), 5 ); this.AddElementFieldMapping( "SalesContractEntity", "CreatedDate", "CREATED_DATE", true, "DateTime", 0, 0, 0, false, "", null, typeof(System.DateTime), 6 ); this.AddElementFieldMapping( "SalesContractEntity", "CreatedBy", "CREATED_BY", true, "NVarChar", 8, 0, 0, false, "", null, typeof(System.String), 7 ); this.AddElementFieldMapping( "SalesContractEntity", "RevisedDate", "REVISED_DATE", true, "DateTime", 0, 0, 0, false, "", null, typeof(System.DateTime), 8 ); this.AddElementFieldMapping( "SalesContractEntity", "RevisedBy", "REVISED_BY", true, "NVarChar", 8, 0, 0, false, "", null, typeof(System.String), 9 ); this.AddElementFieldMapping( "SalesContractEntity", "Closed", "CLOSED", true, "NVarChar", 1, 0, 0, false, "", new ISL.TypeConverters.BooleanStringConverter(), typeof(System.String), 10 ); }
與NHiberate不同，LLBL Gen Pro將對象關系映射直接存儲在源代碼中，數據表字段與實體屬性的映射由代碼生成工具維護。
1.3 數據讀寫 Data access
能過以下幾行簡單的代碼例子，了解LLBL Gen Pro提供的數據訪問接口，下面的代碼適用於Adapter模式。
//讀取實體 DataAccessAdapter adapter... SalesContractEntity salesContract = new SalesContractEntity("SC201507260001"); adapter.FetchEntity(salesContract, prefetchPath, null, fieldList); //保存實體 DataAccessAdapter adapter... SalesContractEntity salesContract =new SalesContractEntity("SC201507260001"); salesContract .Customer="FLEXTRONICS"; adapter.SaveEntity(salesContract , true, false); //刪除實體 DataAccessAdapter adapter... SalesContractEntity salesContract... adapter.DeleteEntity(salesContract);
DataAccessAdapter 是LLBL Gen Pro生成的項目DatabaseSpecific中的一個類型定義，是Adapter模式下標准的數據訪問接口。
2 數據訪問接口 Data access adapter
DataAccessAdapter 對Adapter模式，這個類型是數據訪問接口的全部。如果是自治(SelfServicing)模式，則數據的增刪改方法會直接附加到實體類型定義中。
EntityCollection 對象集合 實體的容器，一般用於數據設計時綁定和實體集的表示。有泛型和非泛型兩個版本。
泛型版本的創建例子如下代碼所示：
EntityCollection collection = new EntityCollection(new SalesContractEntityFactory());
EntityState 對象的狀態 參考下面的枚舉類型定義，對象可處於4種狀態，New表示對象在內存中剛剛創建，Fetched表示對象從數據庫中剛剛取到內存，OutOfSync表示對象的值與數據庫中的值不一致，Deleted表示對象已經被刪除。
public enum EntityState { New, Fetched, OutOfSync, Deleted, }
事務 為保證數據操作中發生異常的回滾操作，事務的例子代碼如下所示。
try { adapter.StartTransaction(IsolationLevel.ReadCommitted, "Post SalesContract"); adapter.DeleteEntity(SalesContract); adapter.Commit(); } catch { adapter.Rollback(); throw; }
存儲過程 LLBL Gen Pro支持兩種存儲過程，一種需要返回值的定義為RetrievalProcedures，另一種是執行數據操作不返回結果的ActionProcedures。
數據庫連接 類型DataAccessAdapter封裝了數據訪問接口，比如打開與關閉數據庫連接，開啟事務。
adapter.OpenConnection(); adapter.CloseConnection();
3 對象關系映射 Object relational mapping
3.1 屬性映射 property mapping
以銷售合同表(SLORDR)的客戶編號(Customer_No)，客戶名稱(Customer_Name)，合同日期(Contract_Date)三個字段為例子，參考下面的屬性與數據表字段定義的映射。
/// <summary> The CustomerNo property of the Entity SalesContract<br/> /// Mapped on table field: "SLORDR"."CUSTOMER_NO"<br/> /// Table field type characteristics (type, precision, scale, length): NVarChar, 0, 0, 8<br/> /// Table field behavior characteristics (is nullable, is PK, is identity): true, false, false<br/><br/></summary> /// <remarks>Mapped on table field: "SLORDR"."CUSTOMER_NO"<br/> /// Table field type characteristics (type, precision, scale, length): NVarChar, 0, 0, 8<br/> /// Table field behavior characteristics (is nullable, is PK, is identity): true, false, false</remarks> public virtual System.String CustomerNo { get { return (System.String)GetValue((int)SalesContractFieldIndex.CustomerNo, true); } set { SetValue((int)SalesContractFieldIndex.CustomerNo, value); } } /// <summary> The CustomerName property of the Entity SalesContract<br/> /// Mapped on table field: "SLORDR"."CUSTOMER_NAME"<br/> /// Table field type characteristics (type, precision, scale, length): NVarChar, 0, 0, 50<br/> /// Table field behavior characteristics (is nullable, is PK, is identity): true, false, false<br/><br/></summary> /// <remarks>Mapped on table field: "SLORDR"."CUSTOMER_NAME"<br/> /// Table field type characteristics (type, precision, scale, length): NVarChar, 0, 0, 50<br/> /// Table field behavior characteristics (is nullable, is PK, is identity): true, false, false</remarks> public virtual System.String CustomerName { get { return (System.String)GetValue((int)SalesContractFieldIndex.CustomerName, true); } set { SetValue((int)SalesContractFieldIndex.CustomerName, value); } } /// <summary> The ContractDate property of the Entity SalesContract<br/> /// Mapped on table field: "SLORDR"."CONTRACT_DATE"<br/> /// Table field type characteristics (type, precision, scale, length): DateTime, 0, 0, 0<br/> /// Table field behavior characteristics (is nullable, is PK, is identity): true, false, false<br/><br/></summary> /// <remarks>Mapped on table field: "SLORDR"."CONTRACT_DATE"<br/> /// Table field type characteristics (type, precision, scale, length): DateTime, 0, 0, 0<br/> /// Table field behavior characteristics (is nullable, is PK, is identity): true, false, false</remarks> public virtual System.DateTime ContractDate { get { return (System.DateTime)GetValue((int)SalesContractFieldIndex.ContractDate, true); } set { SetValue((int)SalesContractFieldIndex.ContractDate, value); } }
LLBL Gen Pro框架依據表的主鍵生成實體的構造方法，設置主鍵字段的元數據，而不像NHibernate那樣，為每個實體生成一個Id主鍵，參考下面的代碼，重寫對象的ToString方法，返回主鍵值。
public override string ToString() { List<string> builder = new List<string>(); foreach (IEntityField2 field2 in Fields) { if (field2.IsPrimaryKey) builder.Add(Convert.ToString(field2.CurrentValue)); } return string.Join(",", builder.ToArray()); }
實體對象繼承於CommonEntityBase，CommonEntityBase繼承於EntityBase2，EntityBase2又繼承於IEntity2。
public abstract class EntityBase2 : IEntity2, IEntityCore, IEditableObject, IActiveContextParticipant, ITransactionalElement, ISerializable, IXmlSerializable, INotifyPropertyChanged, IDataErrorInfo, IEntityCoreInternal { }
這里需要注意一下為什么有此類型的定義后面會加數字2，這是為了支持兩種模式的實體類型定義。
SelfServicing 模式的實體定義接口是IEntity，Adapter模式的實體定義接口是IEntity2。在整個LLBL Gen Pro框架中，凡是與Adapter模式相關的基類會在類型后面加一個數字2，比如上面定義的EntityBase2 。
LLBL Gen Pro不支持實體對象的繼承，數據庫表生成的實體之間都是平行的關系。當然也可以用面向對象的方式編程，增加一個類型繼承於實體類型定義，但不推薦這樣的寫法。
3.2 對象生命周期 Object lifecycle
事件 Events
- Entity: Initializing 實體初始化前
- Entity: Initialized 實體初始化完成
- Entity collection: EntityRemoving 實體集合中的實體刪除前
- Entity collection: EntityRemoved 實體集合中的實體刪除完成(Remove或RemoveAt)
- Entity collection: EntityAdding 實體集合增加實體前
- Entity collection: EntityAdded 實體集合增加實體完成
重寫方法 Overridable methods
- Entity: OnFieldsCreated(僅適用於SelfServicing) 字段創建完成
- Entity: OnFieldValueChanged 實體值更改完成。
- Entity: OnGetValue 獲取值。
- Entity: OnGetValueComplete 獲取值完成 。
- Entity: OnInitializing 實體初始化
- Entity: OnInitialized 初始化完成.
- Entity: OnInitClassMembersComplete 初始化類成員完成。
- Entity: OnRelatedEntitySet 相關實體設置.
- Entity: OnRelatedEntityUnset 相關實體完成
- Entity: OnSetValue 屬性設置值
- Entity: OnSetValueComplete 設置值完成.
- Entity (adapter): OnBeforeEntitySave 實體保存前
- Entity / entity collection: OnGetObjectData 序列化時
- Entity / entity collection: OnDeserialized 反序列化完成。
- Entity collection: OnEntityRemoving 被刪除時。
- Entity collection: OnEntityRemoved 實體集合中的實體刪除后。
- Entity collection: OnEntityAdding 實體集合中增加實體前。
- Entity collection: OnEntityAdded 實體集合中增加實體后.
- DataAccessAdapter: OnInsertPersistenceInfoObjects
- TypedList: OnResultsetBuilt
- TypedList: OnRelationSetBuilt
- TypedList: OnInitialized
- TypedView: OnInitialized
3.3 實體驗證 Entity validate
在實體初始化類型定義中，指定驗證類型，參考下面的代碼。
this.Validator =new SalesContractValidator();
SalesContractValidator驗證類型的完整代碼，主要重寫了保存前驗證和客戶編號值賦值驗證。
[Serializable] public partial class SalesContractValidator : ValidatorBase { // Add your own validation code between the two region markers below. You can also use a partial class and add your overrides in that partial class. // __LLBLGENPRO_USER_CODE_REGION_START ValidationCode public override void ValidateEntityBeforeSave(IEntityCore involvedEntity) { base.ValidateEntityBeforeSave(involvedEntity); SalesContractEntity salesContract = (SalesContractEntity)involvedEntity; if (string.IsNullOrEmpty(salesContract.ContractNo)) throw new EntityValidationException("Contract No. is required"); if (string.IsNullOrEmpty(salesContract.CustomerNo)) throw new EntityValidationException("Customer No. is required"); if (salesContract.IsNew) { ISalesContractManager salesContractManager = ClientProxyFactory.CreateProxyInstance<ISalesContractManager>(); if (salesContractManager.IsSalesContractExist(Shared.CurrentUserSessionId, salesContract.ContractNo)) throw new RecordDuplicatedException(salesContract.ContractNo, "Cotract No. is already used"); } } public override bool ValidateFieldValue(IEntityCore involvedEntity, int fieldIndex, object value) { bool result = base.ValidateFieldValue(involvedEntity, fieldIndex, value); if (!result) return false; switch ((SalesContractFieldIndex) fieldIndex) { case SalesContractFieldIndex.CustomerNo: return this.ValidateCustomerNo((string) value); } return true; } private bool ValidateCustomerNo(string value) { if (!string.IsNullOrEmpty(value)) { ICustomerManager customerManager = ClientProxyFactory.CreateProxyInstance<ICustomerManager>(); customerManager.ValidateCustomerNo(Shared.CurrentUserSessionId, value); } return true; } // __LLBLGENPRO_USER_CODE_REGION_END
4 對象關系 Object relation
1 主從關系 Mater/Detail
LLBL Gen Pro根據表之間的主從關系，在生成源代碼時已經構建好了對象之間的關系。從表會增加一個集合屬性(EntityCollection)到主表所映射的類型中，同時從表也有一個主表的屬性方便引用主表的字段(屬性)。
以銷售合同為例子，一個銷售合同包含多個銷售訂單，銷售合同與銷售訂單是一對多關系。銷售合同的源代碼定義文件：
[Serializable] public partial class SalesContractEntity : CommonEntityBase // __LLBLGENPRO_USER_CODE_REGION_START AdditionalInterfaces // __LLBLGENPRO_USER_CODE_REGION_END { #region Class Member Declarations private EntityCollection<SalesContractDetailEntity> _salesContractDetail; // __LLBLGENPRO_USER_CODE_REGION_START PrivateMembers // __LLBLGENPRO_USER_CODE_REGION_END #endregion
在查詢時，要查詢出銷售合同和它的銷售訂單明細表，可參考下面的代碼。
IPrefetchPath2 prefetchPath = new PrefetchPath2((int) EntityType.SalesContractEntity); prefetchPath.Add(SalesContractEntity.PrefetchPathSalesContractDetail); SalesContractEntity salesContract = _salesContractEntityManager.GetSalesContract("SC201507270001", prefetchPath);
IPrefetchPath2用於LLBL Gen Pro關系查詢，再來看一個三層結構的查詢例子：
IPrefetchPathElement2 prefetchElement = prefetchPath.Add(SalesOrderEntity.PrefetchPathSalesOrderDetails); prefetchElement.SubPath.Add(SalesOrderDetailEntity.PrefetchPathSalesOrderOrderLots);
第一層表是銷售訂單SalesOrder，第二層是銷售訂單明細(物料編號，數量，單價)，第三層是銷售訂單物料明細下的批號(Lot)。對於數據關系中已經建立好的關系，LLBL Gen Pro都會為我們生成關系的類型定義，也支持通過代碼構建關系，參考下面的查詢語句。
IEntityRelation entityRelation = new EntityRelation(OrderLinkFields.OrderNo, JobOrderFields.JobNo, RelationType.OneToMany);
IRelationPredicateBucket filterBucket.Relations.Add(entityRelation);
2 關系類型 Entity relation
先來看一下LLBL Gen Pro定義的關系類型，參考下面的枚舉定義。
public enum RelationType { OneToMany, OneToOne, ManyToOne, ManyToMany, }
實際應用中多對多關系的例子比較少，多對多的關系應該要考慮增加數據表，分解成一對多的關系。
5 數據查詢 Query
5.1 SELECT子句
認識兩個類型ExcludeFieldsList和IncludeFieldsList，及以ExcludeIncludeFieldsList。從名稱中可以推測出類型的含義，IncludeFieldsList是包含要選擇的字段，ExcludeFieldsList是排除不讀取的字段，ExcludeIncludeFieldsList通過傳入構造方法參數，簡化以上兩個類型的的使用。比如下面的代碼，是讀取指定的字段：
ExcludeIncludeFieldsList custSepcFieldList = new ExcludeIncludeFieldsList(false); custSepcFieldList.Add(CustomerSpecificationFields.Description); custSepcFieldList.Add(CustomerSpecificationFields.SalesUom); custSepcFieldList.Add(CustomerSpecificationFields.LotSize); custSepcFieldList.Add(CustomerSpecificationFields.CustItemNo); custSepcFieldList.Add(CustomerSpecificationFields.Specifications);
翻譯成SQL語句，要選擇的字段(IncludeFieldsList)，比如讀取客戶編號和客戶名稱:
SELECT CustomerNo,CustomerName
排除不讀取的字段，比如物料主檔中圖片比較大，SELECT語句中不包含圖片字段，就需要用這個類型的寫法。
除非真的需要，盡量不要寫SELECT * 讀取所有字段。
5.2 FROM子句
LLBL Gen Pro根據讀取的數據類型(Entity,TypeList) 自動生成FROM部分。參考讀取一個實體的代碼：
CustomerSpecificationEntity customerSpec = new CustomerSpecificationEntity(customerNo, itemNo); adapter.FetchEntity(customerSpecificationEntity, prefetchPath, null, fieldList);
再看下面讀取一個列表(TypeList)的寫法，返回一個結果集DataTable。
ResultsetFields fields = new ResultsetFields(1); fields.DefineField(JobOrderFields.JobNo, 0); IRelationPredicateBucket bucket = new RelationPredicateBucket(); bucket.PredicateExpression.Add(JobOrderFields.Posted == true); bucket.PredicateExpression.Add(JobOrderFields.Finished == true); bucket.PredicateExpression.Add(JobOrderFields.Closed == false); System.Data.DataTable table = queryManager.GetQueryResult(fields, bucket, null, null, true, false);
5.3 WHERE 子句與條件表達式
IRelationPredicateBucket類型是SQL中WHERE語句部分的面向對象封裝，IRelationPredicateBucket包含條件和關系，IPredicateExpression 只包含條件，IEntityRelation只包含關系。
IPredicateExpression 舉例如下，
IPredicateExpression B = ((Table1Fields.Foo == "One") & (Table1Fields.Bar == "Two")) // A | (Table2Fields.Bar2 == "Three");
LLBL Gen Pro官方幫助文件中列舉了一個詳細的SQL語句與查詢類型中的映射關系，摘要如下。
| SQL 語句 |
Predicate派生類型 |
| Field BETWEEN 3 AND 5 |
|
| Field = Field2 |
|
| Field Is NULL |
|
| Field IN (1, 2, 3, 5) |
|
| Field IN ( |
|
| Field = 3 |
|
| Field LIKE "Foo%" |
再來看一下關系，如果是在數據庫中有建立表之間的主從關系，則可直接用LLBL Gen Pro生成的關系類型，比如一個客戶可對應多個聯系地址，客戶與聯系地址是一對多的關系：
CustomerEntity.Relations.CustomerContactEntityUsingCustomerNo
如果沒有在數據庫中建立關系，則需要通過IEntityRelation類型創建關系，參看下面的例子代碼。
IEntityRelation entityRelation = new EntityRelation(JobOrderMaterialLedgerFields.JobNo, JobOrderMaterialFields.JobNo, RelationType.OneToMany);
5.4 數據排序 ORDER BY
ISortExpression接口用於封裝排序相關的操作，參考下面的例子。
ISortExpression sortExpression = new SortExpression();
sortExpression.Add(SalesOrderFields.OrderNo | SortOperator.Ascending);
支持多個字段排序，排序優先級與排序字段的增加順序有關。
5.5 數據分組 GROUP BY
IGroupByCollection接口封裝分組相關的操作。來看一個例子代碼，創建分組接口的實例。
IGroupByCollection groupBy = new GroupByCollection(SalesOrderFields.OrderNo);
支持多個字段分組，可以借用下面的代碼來創建多個字段分組的查詢。
IGroupByCollection groupByClause = new GroupByCollection();
groupByClause.Add(JobOrderFields.JobNo);
groupByClause.Add(JobOrderFields.BomNo);
5.6 聚合函數 Aggregate functions
LLBL Gen Pro幫助文檔中有一篇《Generated code - Field expressions and aggregates》是專門講解聚合函數的，參考下面簡單的例子。
ResultsetFields fields = new ResultsetFields(2); fields.DefineField(CustomerFieldIndex.Country, 0, "Country"); fields.DefineField(CustomerFieldIndex.CustomerID, 1, "AmountCustomers"); fields[1].AggregateFunctionToApply = AggregateFunction.CountDistinct;
也可以直接讀取數據，求一個聚合函數的返回值，例子代碼如下。
DataAccessAdapter adapter = new DataAccessAdapter(); decimal orderPrice = (decimal)adapter.GetScalar(OrderDetailsFields.OrderId, (OrderDetailsFields.Quantity * OrderDetailsFields.UnitPrice), AggregateFunction.Sum, (OrderDetailsFIelds.OrderId == 10254));
5.7 子查詢 Subquery
先看SQL語句，讀取客戶編號和它的訂單數量。
SELECT CustomerID, ( SELECT COUNT(*) FROM Orders WHERE CustomerID = Customers.CustomerID ) AS NumberOfOrders FROM Customers
用LLBL Gen Pro Adapter模式實現，代碼如下：
ResultsetFields fields = new ResultsetFields(2); fields.DefineField(CustomerFields.CustomerID, 0); fields.DefineField(new EntityField2("NumberOfOrders", new ScalarQueryExpression(OrderFields.OrderId.SetAggregateFunction(AggregateFunction.Count), (CustomerFields.CustomerId == OrderFields.CustomerId))), 1); DataTable results = new DataTable(); adapter.FetchTypedList(fields, results, null);