TClientDataSet[7]: 辨析 Field、FieldDef、Fields、FieldDefs、FieldList、FieldDefList

TField	TFieldDef	TFields	TFieldDefs	TFieldList、TFieldDefList
Assign AssignValue Clear FocusControl GetData GetParentComponent HasParent IsBlob IsValidChar RefreshLookupList SetData SetFieldType SetParentComponent Validate AsBCD AsBoolean AsCurrency AsDateTime AsSQLTimeStamp AsSQLTimeStampOffset AsSingle AsFloat AsExtended AsInteger AsLargeInt AsString AsWideString AsAnsiString AsBytes AsVariant AttributeSet Calculated CanModify CurValue DataSet DataSize DataType DisplayName DisplayText EditMask EditMaskPtr FieldNo FullName IsIndexField IsNull Lookup LookupList NewValue Offset OldValue ParentField Size Text ValidChars Value Alignment AutoGenerateValue CustomConstraint ConstraintErrorMessage DefaultExpression DisplayLabel DisplayWidth FieldKind FieldName HasConstraints Index ImportedConstraint LookupDataSet LookupKeyFields LookupResultField KeyFields LookupCache Origin ProviderFlags ReadOnly Required Visible OnChange OnGetText OnSetText OnValidate	AddChild Assign CreateField HasChildDefs FieldClass FieldNo InternalCalcField ParentDef Required Attributes ChildDefs DataType Precision Size Name GetNamePath Collection ID Index DisplayName	Add CheckFieldName CheckFieldNames Clear FindField FieldByName FieldByNumber GetEnumerator GetFieldNames IndexOf Remove Count DataSet Fields	AddFieldDef Find Update Add GetItemNames IndexOf Owner Assign BeginUpdate Clear Delete EndUpdate FindItemID GetEnumerator GetNamePath Insert HiddenFields Items ParentDef DataSet Updated Capacity Count ItemClass	FieldByName Find Fields(FieldDefs) Update DataSet Add AddObject Clear Delete Exchange IndexOf Insert InsertObject Sort CustomSort Append AddStrings Assign BeginUpdate EndUpdate Equals GetEnumerator GetText IndexOfName IndexOfObject LoadFromFile LoadFromStream Move SaveToFile SaveToStream SetText Duplicates Sorted CaseSensitive Capacity CommaText Count Delimiter DelimitedText LineBreak Names Objects QuoteChar Values ValueFromIndex NameValueSeparator StrictDelimiter Strings Text StringsAdapter OnChange OnChanging OwnsObjects

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发现这些东西早在 Delphi 3 的时候就比较成熟了, 至今也基本没有变化; 我暂时对它们的理解是:

1、Fields 是 Field 的集合, 它们主要用于运行时对字段元数据和字段值的访问.

2、FieldDefs 是 FieldDef 的集合, 它们主要用于构建数据集(表)和对字段元数据的访问.

3、FieldList 和 FieldDefList 分别是访问 Field 和 FieldDef 的快捷列表; 主要使用其 FieldByName、Find 方法和默认的数组属性访问数据; 它们是只读的.

4、通过 Fields、FieldList、Field 可以得到更多信息, 但必须是在数据集打开的情况下;
通过 FieldDefs、FieldDefList、FieldDef 只能获取定义时的信息, 但即使在数据集关闭时也能使用.

5、顾名思义 FieldDef 是用于定义表的, 但通过 Field 也可以定义表;
用 FieldDef 定义表很方便, 用 Field 可以定义一些更复杂的表;
每个 FieldDef 都会对应一个 Field, 但一个 Field 不一定有 FieldDef 对应;
程序运行后 FieldDef 不能再改变, 而 Field 与 Fields 则可以动态改变或增减.

设计时两者是结合使用的.

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下面是通过三种方法动态建表的代码:

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//使用 TFieldDef 建表:
begin
  with ClientDataSet1.FieldDefs do
  begin
    Add('Name', ftString, 12, True); { True 表示是必填字段 }
    Add('Age', ftInteger);
  end;
  ClientDataSet1.CreateDataSet;
end;

//使用 TField(这里是用其子类)建表:
begin
  with TStringField.Create(Self) do
  begin
    FieldName := 'Name';
    Size := 12;
    Required := True; { 必填字段 }
    DataSet := ClientDataSet1;
  end;
  with TIntegerField.Create(Self) do
  begin
    FieldName := 'Age';
    DataSet := ClientDataSet1;
  end;
  ClientDataSet1.CreateDataSet;
end;

//混合使用(这好像就是设计时的情形):
var
  F: TIntegerField;
begin
  with ClientDataSet1.FieldDefs.AddFieldDef do
  begin
    Name := 'Name';
    DataType := ftString;
    Size := 12;
    Required := True;
    CreateField(ClientDataSet1);
  end;
  with ClientDataSet1.FieldDefs.AddFieldDef do
  begin
    Name := 'Age';
    DataType := ftInteger;
    { 指定最大值和最小值 }
    F := CreateField(ClientDataSet1) as TIntegerField;
    F.MinValue := 0;
    F.MaxValue := 150;
  end;
  ClientDataSet1.CreateDataSet;
end;

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字段类型列表:

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TStringField          { ftString         ; String }
TWideStringField      { ftWideString     ; WideString }
TNumericField         { }
TIntegerField         { ftInteger        ; Integer }
TLongWordField        { ftLongWord       ; LongWord }
TSmallintField        { ftSmallint       ; Smallint }
TShortintField        { ftShortint       ; Shortint }
TByteField            { ftByte           ; Byte }
TLargeintField        { ftLargeint       ; Int64 }
TWordField            { ftWord           ; Word }
TAutoIncField         { ftAutoInc        ; Integer }
TUnsignedAutoIncField { ftAutoInc        ; Cardinal }
TFloatField           { ftFloat          ; Double }
TSingleField          { ftSingle         ; Single }
TCurrencyField        { ftCurrency       ; Currency }
TExtendedField        { ftExtended       ; Extended }
TBooleanField         { ftBoolean        ; WordBool }
TDateTimeField        { ftDateTime       ; DateTime }
TSQLTimeStampField    { ftTimeStamp      ; TSQLTimeStamp }
TSQLTimeStampField    { ftTimeStampOffset; TSQLTimeStampOffset }
TDateField            { ftDate           ; Integer }
TTimeField            { ftTime           ; Integer }
TBinaryField          { }
TBytesField           { ftBytes          ; * }
TVarBytesField        { ftVarBytes       ; * }
TBCDField             { ftBCD            ; * }
TFMTBCDField          { ftFMTBCD         ; * }
TBlobField            { ftBlob           ; * }
TMemoField            { ftMemo           ; * }
TWideMemoField        { ftWideMemo       ; * }
TGraphicField         { ftGraphic        ; * }
TObjectField          { }
TADTField             { ftADT            ; * }
TArrayField           { ftArray          ; * }
TDataSetField         { ftDataSet        ; TDataSet }
TReferenceField       { ftReference      ; * }
TVariantField         { ftVariant        ; OleVariant }
TInterfaceField       { ftInterface      ; IUnknown }
TIDispatchField       { ftIDispatch      ; IDispatch }
TGuidField            { ftGuid           ; TGUID }
TAggregateField       { ftUnknown        ; * }

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