TParams¶

A collection of parameter values for SQL-based datasets.

Declaration¶

Source position: db.pas line 1525

type

  TParams = class(TCollection)
  public
    constructor Create(AOwner: TPersistent; 
                  AItemClass: TCollectionItemClass); overload;
    constructor Create(AOwner: TPersistent); overload;
    constructor Create; overload;
    procedure AddParam;
    procedure AssignValues;
    function CreateParam : TParam;
    function FindParam : TParam;
    procedure GetParamList;
    function IsEqual : Boolean;
    function GetEnumerator : TParamsEnumerator;
    function ParamByName : TParam;
    function ParseSQL(const SQL: string; DoCreate: Boolean) : string; overload;
    function ParseSQL(const SQL: string; DoCreate: Boolean; 
                 EscapeSlash: Boolean; EscapeRepeat: Boolean; 
                 ParameterStyle: TParamStyle) : string; overload;
    function ParseSQL(const SQL: string; DoCreate: Boolean; 
                 EscapeSlash: Boolean; EscapeRepeat: Boolean; 
                 ParameterStyle: TParamStyle; 
                 out ParamBinding: TParamBinding) : string; overload;
    function ParseSQL(const SQL: string; DoCreate: Boolean; 
                 EscapeSlash: Boolean; EscapeRepeat: Boolean; 
                 ParameterStyle: TParamStyle; 
                 out ParamBinding: TParamBinding; 
                 out ReplaceString: string) : string; overload;
    function ParseSQL(const SQL: string; Options: TSQLParseOptions; 
                 ParameterStyle: TParamStyle; 
                 out ParamBinding: TParamBinding; MacroChar: char; 
                 out ReplaceString: string) : string;
    procedure RemoveParam;
    procedure CopyParamValuesFromDataset;
    property Dataset: TDataSet; {r}
    property Items[Index : Integer]: TParam; {rw}
    property ParamValues[const  ParamName : string]: Variant; {rw}
  end;

Inheritance¶

Description¶

TParams is a collection of TParam values. It is used to specify parameter values for parameterized SQL statements, but is also used to specify parameter values for stored procedures. Its default property is an array of TParam values. The class also offers a method to scan a SQL statement for parameter names and replace them with placeholders understood by the SQL engine: TParams.ParseSQL.

TDataset itself does not use TParams. The class is provided in the DB unit, so all TDataset descendents that need some kind of parameterization make use of the same interface. The TMasterParamsDataLink class can be used to establish a master-detail relationship between a parameter-aware TDataset instance and another dataset; it will automatically refresh parameter values when the fields in the master dataset change. To this end, the TParams.CopyParamValuesFromDataset method exists.

Properties¶

Member	Visibility	Description
Dataset read only	public	Dataset that owns the TParams instance.
Items	public	Indexed access to TParams instances in the collection.
ParamValues	public	Named access to the parameter values.

See all Properties

Methods¶

Member	Visibility	Description
AddParam	public	Add a parameter to the collection.
AssignValues	public	Copy values from another collection.
CopyParamValuesFromDataset	public	Copy parameter values from the fields in a dataset.
Create	public	Create a new instance of TParams.
CreateParam	public	Create and add a new parameter to the collection.
FindParam	public	Find a parameter with given name.
GetEnumerator	public	Return an enumerator for the parameters.
GetParamList	public	Fetch a list of TParam instances.
IsEqual	public	Is the list of parameters equal.
ParamByName	public	Return a parameter by name.
ParseSQL	public	Parse SQL statement, replacing parameter names with SQL parameter placeholders.
RemoveParam	public	Remove a parameter from the collection.

See all Methods

Name	Description
TDataset	Base class for records-based data-access.
TMasterParamsDataLink	Class to establish a master-detail relationship between dataset, based on parameters.
TParam	Parameter description class.
TParams.ParseSQL	Parse SQL statement, replacing parameter names with SQL parameter placeholders.
TParams.CopyParamValuesFromDataset	Copy parameter values from the fields in a dataset.