delphi 参数化sql

曾经查过资料，后来忘了，现在做一下记录。

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在 sql 语句里占位使用一个冒号和一个用来表示这个位置的符号, 例如：SELECT * FROM aTableName WHERE aCol = :ColVal

SELECT * FROM aTableName WHERE aCol =  :ColVal

对占位了的地方赋值这里使用的是 paremeters 属性的 paramByName 作的, 例如：

LDataSet.Parameters.ParamByName('ColVal').Value := 'SomeValue';

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最近在 Delphi 7 中通过参数化的方式存汉字字符串，出现只存入了一部分的情况，搜索资料并测试之后，发现设置 DataType = ftWideString 可以解决。

示例：

LCommand.Parameters.ParamByName('AKeyName').DataType := ftWideString;
LCommand.Parameters.ParamByName('AKeyName').Value := '我没有，我不是，别瞎说';

DataType 的类型：DB.pas/TFieldType

--date=2019-08-16

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为了使贴出来的代码具有完成性和尽量的简单性, 把以前的代码改写了一下, 现在的代码是控制台程序,

在程序体中对数据库访问代码作了简单的调用.

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今天重新看了一遍代码，发现一个问题，就是程序入口里的变量 QueryResult 所使用过的对象都没有释放！！！

--date=2019-09-11

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数据访问单元的代码：

  1 unit uDBAccesser;
  2 
  3 interface
  4 
  5 uses
  6   System.Generics.Collections, Data.Win.ADODB;
  7 
  8 
  9 type TTAbleInfo = record
 10   DataSource : String;
 11   DbName     : String;
 12   Username   : String;
 13   Password   : String;
 14   Name       : String;
 15   IntCol     : String;
 16   TxtCol     : String;
 17 end;
 18 
 19 type TEntity = record
 20   SomeInt : Integer;
 21   SomeTxt : String;
 22 end;
 23 
 24 type TDBAccesser = class
 25   private
 26     FConn : TADOConnection;
 27 
 28     function Query( const ASql : String; const AParams : TDictionary<String, Variant>) : TList<TEntity>;
 29     // 广泛含义的更新
 30     function Update(Const ASql : String; const AParams : TDictionary<String, Variant>) : Boolean; overload;
 31   public
 32     constructor Create();
 33     destructor  Destroy(); override;
 34 
 35     function QueryAll() : TList<TEntity>;
 36     function QueryByInt(const AInt : Integer) : TList<TEntity>;
 37     function QueryByTxt(const ATxt : String ) : TList<TEntity>;
 38     function InsertOne(const AEntity : TEntity) : Boolean;
 39     function Delete(const AEntity : TEntity) : Boolean;
 40     // 狭义的更新
 41     function Update(const AOldValue : TEntity; const ANewValue : TEntity) : Boolean; overload;
 42 end;
 43 
 44 
 45 var
 46   TableInfo : TTableInfo;
 47 
 48 implementation
 49 
 50 uses
 51   System.SysUtils, System.Variants, Winapi.ActiveX;
 52 
 53 
 54 constructor TDBAccesser.Create();
 55 const  // MS SQL
 56   LConnStrFormat : String = 'provider=SQLOLEDB.1;password=%s;User ID=%s;'
 57                           + 'Initial CataLog=%s;Data source=%s;';
 58 var
 59   LConnStr : String;
 60 begin
 61   try
 62     LConnStr := Format(LConnStrFormat, [TableInfo.Password, TableInfo.Username,
 63                                         TableInfo.DbName, TableInfo.DataSource]);
 64 
 65     Self.FConn := TADOConnection.Create(nil);
 66     Self.FConn.ConnectionString := LConnStr;
 67     Self.FConn.LoginPrompt := False;
 68     Self.FConn.Connected   := True;
 69   except
 70     on Err : Exception do begin
 71       FreeAndNil(Self.FConn);
 72       WriteLn('Error on create DBAccesser: ' + Err.Message);
 73     end;
 74   end;
 75 end;
 76 
 77 destructor TDBAccesser.Destroy;
 78 begin
 79   FreeAndNil(Self.FConn);
 80 end;
 81 
 82 
 83 function TDBAccesser.Query(const ASql: string; const AParams: TDictionary<System.string,System.Variant>) : TList<TEntity>;
 84 var
 85   LDataSet : TADODataSet;
 86   LRow : TEntity;
 87   LKey : String;
 88 begin
 89   LDataSet := nil;
 90   try
 91     LDataSet := TADODataSet.Create(nil);
 92     LDataSet.Connection  := Self.FConn;
 93     LDataSet.CommandText := ASql;
 94 
 95     // 我印象有篇文章说这句必须要有, 但不写也没发现问题
 96     LDataSet.Parameters.ParseSQL(LDataSet.CommandText, True);
 97     if (AParams <> nil) then begin
 98       for LKey in AParams.Keys do begin
 99         LDataSet.Parameters.ParamByName(LKey).Value := AParams.Items[LKey];
100       end;
101     end;
102 
103     LDataSet.Open;
104     LDataSet.First;
105 
106     Result := TList<TEntity>.Create();
107     while not LDataSet.Eof do begin
108       LRow.SomeInt := LDataSet.FieldByName(TableInfo.IntCol).AsInteger; // 也可以这种格式 LDataSet.Fields[0].AsBoolean;
109       LRow.SomeTxt := LDataSet.FieldByName(TableInfo.TxtCol).AsString;
110 
111       Result.Add(LRow);
112 
113       LDataSet.Next;
114     end;
115   finally
116     FreeAndNil(LDataSet);
117   end;
118 end;
119 
120 function TDBAccesser.Update(Const ASql : String; const AParams : TDictionary<String, Variant>) : Boolean;
121 var
122   LCmd : TADOCommand;
123   LKey : String;
124   LRowsAffected : Integer;
125 begin
126   Result := False;
127   LCmd := nil;
128   try
129     LCmd := TADOCommand.Create(nil);
130     LCmd.Connection  := Self.FConn;
131     LCmd.CommandText := ASql;
132 
133     LCmd.Parameters.ParseSQL(LCmd.CommandText, True);
134 
135     if (AParams <> nil) then begin
136       for LKey in AParams.Keys do begin
137         LCmd.Parameters.ParamByName(LKey).Value := AParams.Items[LKey];
138       end;
139     end;
140 
141     // 也可以直接在 EmptyParam 的位置直接写 [Param1, Param2, ...] 格式的内容，
142     // 而不使用上面的 Parameters，两者不能同时使用，
143     // 但具体什么情况我也忘了，相应代码也找不到了，要想知道真实情况，还得再动手去摸索
144     LCmd.Execute(LRowsAffected, EmptyParam);
145 
146     if (LRowsAffected > 0) then begin
147       Result := True;
148     end
149     else begin
150       Result := False;
151     end;
152   finally
153     FreeAndNil(LCmd);
154   end;
155 end;
156 
157 
158 function TDBAccesser.QueryAll() : TList<TEntity>;
159 const
160   LSqlFormat : String = 'SELECT %s, %s FROM %s';
161 var
162   LSql : String;
163 begin
164   LSql := Format(LSqlFormat, [TableInfo.TxtCol, TableInfo.IntCol, TableInfo.Name]);
165 
166   Result := Self.Query(LSql, nil);
167 end;
168 
169 function TDBAccesser.QueryByInt(const AInt: Integer) : TList<TEntity>;
170 const
171   LSqlFormat : String = 'SELECT %s, %s FROM %s WHERE %s = :$Int ';
172 var
173   LSql : String;
174   LParams : TDictionary<String, Variant>;
175 begin
176   LParams := TDictionary<String, Variant>.Create();
177   try
178     LSql := Format(LSqlFormat, [TableInfo.TxtCol, TableInfo.IntCol,
179                                 TableInfo.Name, TableInfo.IntCol]);
180 
181     LParams.Add('$Int', AInt);
182 
183     Result := Self.Query(LSql, LParams);
184   finally
185     FreeAndNil(LParams);
186   end;
187 end;
188 
189 function TDBAccesser.QueryByTxt(const ATxt: String) : TList<TEntity>;
190 const
191   LSqlFormat : String = 'SELECT %s, %s FROM %s WHERE %s = :$Txt ';
192 var
193   LSql : String;
194   LParams : TDictionary<String, Variant>;
195 begin
196   LParams := TDictionary<String, Variant>.Create();
197   try
198     LSql := Format(LSqlFormat, [TableInfo.TxtCol, TableInfo.IntCol,
199                                 TableInfo.Name, TableInfo.TxtCol]);
200 
201     LParams.Add('$Txt', ATxt);
202 
203     Result := Self.Query(LSql, LParams);
204   finally
205     FreeAndNil(LParams);
206   end;
207 end;
208 
209 function TDBAccesser.InsertOne(const AEntity: TEntity) : Boolean;
210 const
211   LSqlFormat : String = 'INSERT INTO %s (%s, %s) '
212                       + 'VALUES (:$Txt, :$Int) ';
213 var
214   LSql : String;
215   LParams : TDictionary<String, Variant>;
216 begin
217   LParams := TDictionary<String, Variant>.Create();
218   try
219     LSql := Format(LSqlFormat, [TableInfo.Name, TableInfo.TxtCol, TableInfo.IntCol]);
220 
221     LParams.Add('$Txt', AEntity.SomeTxt);
222     LParams.Add('$Int', AEntity.SomeInt);
223 
224     Result := Self.Update(LSql, LParams);
225   finally
226     FreeAndNil(LParams);
227   end;
228 end;
229 
230 function TDBAccesser.Delete(const AEntity: TEntity) : Boolean;
231 const
232   LSqlFormat : String = 'DELETE FROM %s '
233                       + 'WHERE %s = :$Txt AND %s = :$Int ';
234 var
235   LSql : String;
236   LParams : TDictionary<String, Variant>;
237 begin
238   LParams := TDictionary<String, Variant>.Create();
239   try
240     LSql := Format(LSqlFormat, [TableInfo.Name, TableInfo.TxtCol, TableInfo.IntCol]);
241 
242     LParams.Add('$Txt', AEntity.SomeTxt);
243     LParams.Add('$Int', AEntity.SomeInt);
244 
245     Result := Self.Update(LSql, LParams);
246   finally
247     FreeAndNil(LParams);
248   end;
249 end;
250 
251 function TDBAccesser.Update(const AOldValue: TEntity; const ANewValue: TEntity) : Boolean;
252 const
253   LSqlFormat : String = 'UPDATE %s '
254                       + 'SET %s = :$TxtVal, %s = :$IntVal '
255                       + 'WHERE %s = :$OldTxtVal AND %s = :$OldIntVal ';
256 var
257   LSql : String;
258   LParams : TDictionary<String, Variant>;
259 begin
260   LParams := TDictionary<String, Variant>.Create();
261   try
262     LSql := Format(LSqlFormat, [TableInfo.Name,
263                                 TableInfo.TxtCol, TableInfo.IntCol,
264                                 TableInfo.TxtCol, TableInfo.IntCol]);
265 
266     LParams.Add('$TxtVal', ANewValue.SomeTxt);
267     LParams.Add('$IntVal', ANewValue.SomeInt);
268 
269     LParams.Add('$OldTxtVal', AOldValue.SomeTxt);
270     LParams.Add('$OldIntVal', AOldValue.SomeInt);
271 
272     Result := Self.Update(LSql, LParams);
273   finally
274     FreeAndNil(LParams);
275   end;
276 end;
277 
278 
279 initialization
280   TableInfo.DataSource := '.';
281   TableInfo.DbName     := 'simpleTestByX';
282   TableInfo.Username   := 'sa';
283   TableInfo.Password   := '123456';
284   TableInfo.Name       := 'tab_simple_test';
285   TableInfo.IntCol     := 'some_int';
286   TableInfo.TxtCol     := 'some_txt';
287 
288   CoInitialize(nil);
289 
290 finalization
291   CoUninitialize();
292 
293 
294 end.

控制台程序入口代码，对上面的单元进行简单的调用：

  1 program ProjectParameterizedSql;
  2 
  3 {$APPTYPE CONSOLE}
  4 
  5 {$R *.res}
  6 
  7 uses
  8   System.SysUtils,
  9   System.Generics.Collections,
 10   uDBAccesser in 'uDBAccesser.pas';
 11 
 12 
 13 function FormatEntity(AEntity : TEntity) : String;
 14 begin
 15   Result := Format(' SomeInt = %d, SomeTxt = %s ', [AEntity.SomeInt, AEntity.SomeTxt]);
 16 end;
 17 
 18 
 19 var
 20   DBAccesser      : TDBAccesser;
 21   EntityQuery     : TEntity;
 22   EntityInsert    : TEntity;
 23   EntityDelete    : TEntity;
 24   EntityUpdateNew : TEntity;
 25   EntityUpdateOld : TEntity;
 26   EntityCommon    : TEntity;
 27   QueryResult     : TList<TEntity>;
 28 begin
 29   try
 30     DBAccesser := TDBAccesser.Create();
 31     try
 32       WriteLn('1) insert one: ');
 33 
 34       EntityInsert.SomeInt := 1;
 35       EntityInsert.SomeTxt := 'Hello';
 36       WriteLn('  entity = ', FormatEntity(EntityInsert));
 37 
 38       WriteLn('  insert success? ', DBAccesser.InsertOne(EntityInsert));
 39       WriteLn('----------------');
 40 
 41       WriteLn('2) query all: ');
 42 
 43       QueryResult := DBAccesser.QueryAll();
 44 
 45       WriteLn('  total = ', QueryResult.Count);
 46       for EntityCommon in QueryResult do begin
 47         WriteLn('  ', FormatEntity(EntityCommon));
 48       end;
 49       WriteLn('----------------');
 50 
 51       WriteLn('3) update: ');
 52 
 53       EntityUpdateOld := EntityInsert;
 54       EntityUpdateNew.SomeInt := 2;
 55       EntityUpdateNew.SomeTxt := 'World';
 56 
 57       WriteLn('  old : ', FormatEntity(EntityUpdateOld));
 58       WriteLn('  new : ', FormatEntity(EntityUpdateNew));
 59 
 60       WriteLn('  update success? ', DBAccesser.Update(EntityUpdateOld, EntityUpdateNew));
 61       WriteLn('----------------');
 62 
 63       WriteLn('4) query by int:');
 64 
 65       EntityQuery := EntityUpdateNew;
 66       WriteLn('  int = ', EntityQuery.SomeInt);
 67 
 68       QueryResult := DBAccesser.QueryByInt(EntityQuery.SomeInt);
 69 
 70       WriteLn('  total : ', QueryResult.Count);
 71       for EntityCommon in QueryResult do begin
 72         WriteLn('  ', FormatEntity(EntityCommon));
 73       end;
 74       WriteLn('----------------');
 75 
 76       WriteLn('5) query by txt:');
 77 
 78       EntityQuery := EntityUpdateNew;
 79       WriteLn('  txt = ', EntityQuery.SomeTxt);
 80 
 81       QueryResult := DBAccesser.QueryByTxt(EntityQuery.SomeTxt);
 82 
 83       WriteLn('  total : ', QueryResult.Count);
 84       for EntityCommon in QueryResult do begin
 85         WriteLn('  ', FormatEntity(EntityCommon));
 86       end;
 87       WriteLn('----------------');
 88 
 89       WriteLn('6) delete:');
 90 
 91       EntityDelete := EntityUpdateNew;
 92       WriteLn('  entity = ', FormatEntity(EntityDelete));
 93 
 94       WriteLn('  delete success? ', DBAccesser.Delete(EntityDelete));
 95       WriteLn('----------------');
 96 
 97       WriteLn('7) query all: ');
 98 
 99       QueryResult := DBAccesser.QueryAll();
100       WriteLn('  total : ', QueryResult.Count);
101       for EntityCommon in QueryResult do begin
102         WriteLn('  ', FormatEntity(EntityCommon));
103       end;
104       WriteLn('----------------');
105 
106       WriteLn('--- THE END ---');
107     finally
108       FreeAndNil(DBAccesser);
109     end;
110   except
111     on E: Exception do
112       Writeln(E.ClassName, ': ', E.Message);
113   end;
114   ReadLn;
115 end.