有些時(shí)候,sql語句where條件中,需要一些安全判斷,例如按某一條件查詢時(shí)如果傳入的參數(shù)是空,此時(shí)查詢出的結(jié)果很可能是空的,也許我們需要參數(shù)為空時(shí),是查出全部的信息。使用Oracle的序列、mysql的函數(shù)生成Id。這時(shí)我們可以使用動態(tài)sql。
下文均采用mysql語法和函數(shù)(例如字符串鏈接函數(shù)CONCAT)。
selectKey 標(biāo)簽
在insert語句中,在Oracle經(jīng)常使用序列、在MySQL中使用函數(shù)來自動生成插入表的主鍵,而且需要方法能返回這個(gè)生成主鍵。使用myBatis的selectKey標(biāo)簽可以實(shí)現(xiàn)這個(gè)效果。
下面例子,使用mysql數(shù)據(jù)庫自定義函數(shù)nextval('student'),用來生成一個(gè)key,并把他設(shè)置到傳入的實(shí)體類中的studentId屬性上。所以在執(zhí)行完此方法后,邊可以通過這個(gè)實(shí)體類獲取生成的key。
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<!-- 插入學(xué)生 自動主鍵--> < insert id = "createStudentAutoKey" parameterType = "bjpowernodestudentmanagerdatamodelStudentEntity" keyProperty = "studentId" > < selectKey keyProperty = "studentId" resultType = "String" order = "BEFORE" > select nextval('student') </ selectKey > INSERT INTO STUDENT_TBL(STUDENT_ID, STUDENT_NAME, STUDENT_SEX, STUDENT_BIRTHDAY, STUDENT_PHOTO, CLASS_ID, PLACE_ID) VALUES (#{studentId}, #{studentName}, #{studentSex}, #{studentBirthday}, #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=orgapacheibatistypeBlobTypeHandler}, #{classId}, #{placeId}) </ insert > |
調(diào)用接口方法,和獲取自動生成key
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StudentEntity entity = new StudentEntity(); entity.setStudentName( "黎明你好" ); entity.setStudentSex( 1 ); entity.setStudentBirthday(DateUtil.parse( "1985-05-28" )); entity.setClassId( "20000001" ); entity.setPlaceId( "70000001" ); this .dynamicSqlMapper.createStudentAutoKey(entity); System.out.println( "新增學(xué)生ID: " + entity.getStudentId()); |
selectKey語句屬性配置細(xì)節(jié):
屬性
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描述
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取值
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keyProperty
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selectKey 語句生成結(jié)果需要設(shè)置的屬性。
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resultType
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生成結(jié)果類型,MyBatis 允許使用基本的數(shù)據(jù)類型,包括String 、int類型。
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order
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1:BEFORE,會先選擇主鍵,然后設(shè)置keyProperty,再執(zhí)行insert語句;
2:AFTER,就先運(yùn)行insert 語句再運(yùn)行selectKey 語句。
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BEFORE
AFTER
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statementType
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MyBatis 支持STATEMENT,PREPARED和CALLABLE 的語句形式, 對應(yīng)Statement ,PreparedStatement 和CallableStatement 響應(yīng)
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STATEMENT
PREPARED
CALLABLE
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if標(biāo)簽
if標(biāo)簽可用在許多類型的sql語句中,我們以查詢?yōu)槔J紫瓤匆粋€(gè)很普通的查詢:
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<!-- 查詢學(xué)生list,like姓名 --> < select id = "getStudentListLikeName" parameterType = "StudentEntity" resultMap = "studentResultMap" > SELECT * from STUDENT_TBL ST WHERE ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%') </ select > 但是此時(shí)如果studentName或studentSex為null,此語句很可能報(bào)錯(cuò)或查詢結(jié)果為空。此時(shí)我們使用if動態(tài)sql語句先進(jìn)行判斷,如果值為null或等于空字符串,我們就不進(jìn)行此條件的判斷,增加靈活性。 參數(shù)為實(shí)體類StudentEntity。將實(shí)體類中所有的屬性均進(jìn)行判斷,如果不為空則執(zhí)行判斷條件。 <!-- 2 if(判斷參數(shù)) - 將實(shí)體類不為空的屬性作為where條件 --> < select id = "getStudentList_if" resultMap = "resultMap_studentEntity" parameterType = "bjpowernode.student.manager.data.model.StudentEntity" > SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST WHERE < if test = "studentName !=null " > ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%') </ if > < if test = "studentSex != null and studentSex != '' " > AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER} </ if > < if test = "studentBirthday != null " > AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE} </ if > < if test = "classId != null and classId!= '' " > AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR} </ if > < if test = "classEntity != null and classEntityclassId !=null and classEntityclassId !=' ' " > AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR} </ if > < if test = "placeId != null and placeId != '' " > AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR} </ if > < if test = "placeEntity != null and placeEntityplaceId != null and placeEntityplaceId != '' " > AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR} </ if > < if test = "studentId != null and studentId != '' " > AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR} </ if > </ select > |
使用時(shí)比較靈活, new一個(gè)這樣的實(shí)體類,我們需要限制那個(gè)條件,只需要附上相應(yīng)的值就會where這個(gè)條件,相反不去賦值就可以不在where中判斷。
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public void select_test_2_1() { StudentEntity entity = new StudentEntity(); entity.setStudentName( "" ); entity.setStudentSex( 1 ); entity.setStudentBirthday(DateUtil.parse( "1985-05-28" )); entity.setClassId( "20000001" ); //entity.setPlaceId("70000001"); List<StudentEntity> list = this .dynamicSqlMapper.getStudentList_if(entity); for (StudentEntity e : list) { System.out.println(e.toString()); } } |
if + where 的條件判斷
當(dāng)where中的條件使用的if標(biāo)簽較多時(shí),這樣的組合可能會導(dǎo)致錯(cuò)誤。我們以在3.1中的查詢語句為例子,當(dāng)java代碼按如下方法調(diào)用時(shí):
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@Test public void select_test_2_1() { StudentEntity entity = new StudentEntity(); entity.setStudentName( null ); entity.setStudentSex( 1 ); List<StudentEntity> list = this .dynamicSqlMapper.getStudentList_if(entity); for (StudentEntity e : list) { System.out.println(e.toString()); } } |
如果上面例子,參數(shù)studentName為null,將不會進(jìn)行STUDENT_NAME列的判斷,則會直接導(dǎo)“WHERE AND”關(guān)鍵字多余的錯(cuò)誤SQL。
這時(shí)我們可以使用where動態(tài)語句來解決。這個(gè)“where”標(biāo)簽會知道如果它包含的標(biāo)簽中有返回值的話,它就插入一個(gè)‘where'。此外,如果標(biāo)簽返回的內(nèi)容是以AND 或OR 開頭的,則它會剔除掉。
上面例子修改為:
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<!-- 3 select - where/if(判斷參數(shù)) - 將實(shí)體類不為空的屬性作為where條件 --> < select id = "getStudentList_whereIf" resultMap = "resultMap_studentEntity" parameterType = "bjpowernode.student.manager.data.model.StudentEntity" > SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST < where > < if test = "studentName !=null " > ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%') </ if > < if test = "studentSex != null and studentSex != '' " > AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER} </ if > < if test = "studentBirthday != null " > AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE} </ if > < if test = "classId != null and classId!= '' " > AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR} </ if > < if test = "classEntity != null and classEntityclassId !=null and classEntityclassId !=' ' " > AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR} </ if > < if test = "placeId != null and placeId != '' " > AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR} </ if > < if test = "placeEntity != null and placeEntityplaceId != null and placeEntityplaceId != '' " > AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR} </ if > < if test = "studentId != null and studentId != '' " > AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR} </ if > </ where > </ select > |
if + set 的更新語句
當(dāng)update語句中沒有使用if標(biāo)簽時(shí),如果有一個(gè)參數(shù)為null,都會導(dǎo)致錯(cuò)誤。
當(dāng)在update語句中使用if標(biāo)簽時(shí),如果前面的if沒有執(zhí)行,則或?qū)е露禾柖嘤噱e(cuò)誤。使用set標(biāo)簽可以將動態(tài)的配置SET 關(guān)鍵字,和剔除追加到條件末尾的任何不相關(guān)的逗號。
使用if+set標(biāo)簽修改后,如果某項(xiàng)為null則不進(jìn)行更新,而是保持?jǐn)?shù)據(jù)庫原值。如下示例:
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<!-- 4 if/set(判斷參數(shù)) - 將實(shí)體類不為空的屬性更新 --> < update id = "updateStudent_if_set" parameterType = "bjpowernode.student.manager.data.model.StudentEntity" > UPDATE STUDENT_TBL < set > < if test = "studentName != null and studentName != '' " > STUDENT_TBL.STUDENT_NAME = #{studentName}, </ if > < if test = "studentSex != null and studentSex != '' " > STUDENT_TBL.STUDENT_SEX = #{studentSex}, </ if > < if test = "studentBirthday != null " > STUDENT_TBL.STUDENT_BIRTHDAY = #{studentBirthday}, </ if > < if test = "studentPhoto != null " > STUDENT_TBL.STUDENT_PHOTO = #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler}, </ if > < if test = "classId != '' " > STUDENT_TBL.CLASS_ID = #{classId} </ if > < if test = "placeId != '' " > STUDENT_TBL.PLACE_ID = #{placeId} </ if > </ set > WHERE STUDENT_TBL.STUDENT_ID = #{studentId}; </ update > |
if + trim代替where/set標(biāo)簽
trim是更靈活的去處多余關(guān)鍵字的標(biāo)簽,他可以實(shí)踐where和set的效果。
trim代替where
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<!-- 5.1 if/trim代替where(判斷參數(shù)) - 將實(shí)體類不為空的屬性作為where條件 --> < select id = "getStudentList_if_trim" resultMap = "resultMap_studentEntity" > SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST < trim prefix = "WHERE" prefixOverrides = "AND|OR" > < if test = "studentName !=null " > ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%') </ if > < if test = "studentSex != null and studentSex != '' " > AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER} </ if > < if test = "studentBirthday != null " > AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE} </ if > < if test = "classId != null and classId!= '' " > AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR} </ if > < if test = "classEntity != null and classEntityclassId !=null and classEntityclassId !=' ' " > AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR} </ if > < if test = "placeId != null and placeId != '' " > AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR} </ if > < if test = "placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' " > AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR} </ if > < if test = "studentId != null and studentId != '' " > AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR} </ if > </ trim > </ select > |
trim代替set
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<!-- 2 if/trim代替set(判斷參數(shù)) - 將實(shí)體類不為空的屬性更新 --> < update id = "updateStudent_if_trim" parameterType = "bjpowernode.student.manager.data.model.StudentEntity" > UPDATE STUDENT_TBL < trim prefix = "SET" suffixOverrides = "," > < if test = "studentName != null and studentName != '' " > STUDENT_TBL.STUDENT_NAME = #{studentName}, </ if > < if test = "studentSex != null and studentSex != '' " > STUDENT_TBL.STUDENT_SEX = #{studentSex}, </ if > < if test = "studentBirthday != null " > STUDENT_TBL.STUDENT_BIRTHDAY = #{studentBirthday}, </ if > < if test = "studentPhoto != null " > STUDENT_TBL.STUDENT_PHOTO = #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler}, </ if > < if test = "classId != '' " > STUDENT_TBL.CLASS_ID = #{classId}, </ if > < if test = "placeId != '' " > STUDENT_TBL.PLACE_ID = #{placeId} </ if > </ trim > WHERE STUDENT_TBLSTUDENT_ID = #{studentId} </ update > |
choose (when, otherwise)
有時(shí)候我們并不想應(yīng)用所有的條件,而只是想從多個(gè)選項(xiàng)中選擇一個(gè)。而使用if標(biāo)簽時(shí),只要test中的表達(dá)式為true,就會執(zhí)行if標(biāo)簽中的條件。MyBatis提供了choose 元素。if標(biāo)簽是與(and)的關(guān)系,而choose比傲天是或(or)的關(guān)系。
choose標(biāo)簽是按順序判斷其內(nèi)部when標(biāo)簽中的test條件出否成立,如果有一個(gè)成立,則choose結(jié)束。當(dāng)choose中所有when的條件都不滿則時(shí),則執(zhí)行otherwise中的sql。類似于Java 的switch 語句,choose為switch,when為case,otherwise則為default。
例如下面例子,同樣把所有可以限制的條件都寫上,方面使用。choose會從上到下選擇一個(gè)when標(biāo)簽的test為true的sql執(zhí)行。安全考慮,我們使用where將choose包起來,放置關(guān)鍵字多于錯(cuò)誤。
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<!-- 6 choose(判斷參數(shù)) - 按順序?qū)?shí)體類第一個(gè)不為空的屬性作為where條件 --> < select id = "getStudentList_choose" resultMap = "resultMap_studentEntity" parameterType = "bjpowernode.student.manager.data.model.StudentEntity" > SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST < where > < choose > < when test = "studentName !=null " > ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%') </ when > < when test = "studentSex != null and studentSex != '' " > AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER} </ when > < when test = "studentBirthday != null " > AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE} </ when > < when test = "classId != null and classId!= '' " > AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR} </ when > < when test = "classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' " > AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR} </ when > < when test = "placeId != null and placeId != '' " > AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR} </ when > < when test = "placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' " > AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR} </ when > < when test = "studentId != null and studentId != '' " > AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR} </ when > < otherwise > </ otherwise > </ choose > </ where > </ select > |
foreach
對于動態(tài)SQL 非常必須的,主是要迭代一個(gè)集合,通常是用于IN 條件。List 實(shí)例將使用“list”做為鍵,數(shù)組實(shí)例以“array” 做為鍵。
foreach元素是非常強(qiáng)大的,它允許你指定一個(gè)集合,聲明集合項(xiàng)和索引變量,它們可以用在元素體內(nèi)。它也允許你指定開放和關(guān)閉的字符串,在迭代之間放置分隔符。這個(gè)元素是很智能的,它不會偶然地附加多余的分隔符。
注意:你可以傳遞一個(gè)List實(shí)例或者數(shù)組作為參數(shù)對象傳給MyBatis。當(dāng)你這么做的時(shí)候,MyBatis會自動將它包裝在一個(gè)Map中,用名稱在作為鍵。List實(shí)例將會以“list”作為鍵,而數(shù)組實(shí)例將會以“array”作為鍵。
這個(gè)部分是對關(guān)于XML配置文件和XML映射文件的而討論的。下一部分將詳細(xì)討論Java API,所以你可以得到你已經(jīng)創(chuàng)建的最有效的映射。
參數(shù)為array示例的寫法
接口的方法聲明:
動態(tài)SQL語句:
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<!— 7.1 foreach(循環(huán)array參數(shù)) - 作為where中in的條件 --> < select id = "getStudentListByClassIds_foreach_array" resultMap = "resultMap_studentEntity" > SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST WHERE STCLASS_ID IN < foreach collection = "array" item = "classIds" open = "(" separator = "," close = ")" > #{classIds} </ foreach > </ select > |
測試代碼,查詢學(xué)生中,在20000001、20000002這兩個(gè)班級的學(xué)生:
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@Test public void test7_foreach() { String[] classIds = { "20000001" , "20000002" }; List<StudentEntity> list = this .dynamicSqlMapper.getStudentListByClassIds_foreach_array(classIds); for (StudentEntity e : list) { System.out.println(e.toString()); } <p>}<span style= "font-size: 14px; font-weight: bold; white-space: normal;" > </span></p> |
參數(shù)為list示例的寫法
接口的方法聲明:
動態(tài)SQL語句:
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<!-- 7.2 foreach(循環(huán)List<String>參數(shù)) - 作為where中in的條件 --> < select id = "getStudentListByClassIds_foreach_list" resultMap = "resultMap_studentEntity" > SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST WHERE STCLASS_ID IN < foreach collection = "list" item = "classIdList" open = "(" separator = "," close = ")" > #{classIdList} </ foreach > </ select > |
測試代碼,查詢學(xué)生中,在20000001、20000002這兩個(gè)班級的學(xué)生:
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@Test public void test7_2_foreach() { ArrayList<String> classIdList = new ArrayList<String>(); classIdList.add( "20000001" ); classIdList.add( "20000002" ); List<StudentEntity> list = this .dynamicSqlMapper.getStudentListByClassIds_foreach_list(classIdList); for (StudentEntity e : list) { System.out.println(e.toString()); } } |