前言：近日遇到很複雜的業務邏輯需要處理（每每這個時候博主經常吐槽自己腦子不夠用了😂），數據庫查詢需要通過不同業務不同條件進行動態拼接，而且涉及數據量巨大，表也關聯的多，這時候明顯xml不適合這個場景，雖然說可以做到，但是麻煩程度絕對大於我接下來的做法，然後不經意間發現下面這種寫法，發現Mybatis挺靈活的。有①xml方式(常用)、②普通註解（@Select、@Insert等），③高級註解（@SelectProvider、@InsertProvider等）④SQL語句構建器類http://www.mybatis.org/mybatis-3/zh/statement-builders.html
…還有其它的方式等我去研究發現嘿嘿，言歸正傳。
假設需求根據給出的條件（此條件不固定），然後關聯幾張表，給我查出我需要的字段（視圖）。看似很簡單的需求，實則深似海哈哈哈
下面貼出代碼（看不太懂的，下面有解釋說明）
/**
* 根據移庫規則表檢查該數據是否可自動生成任務
*
* @param warehouseTransferRuleConfig
* @return
*/
@SelectProvider(type = WarehouseTransferRuleConfigMapperProvider.class, method = "canAutoCreateSourceDetailList")
List<SourceDetail> canAutoCreateSourceDetailList(WarehouseTransferRuleConfig warehouseTransferRuleConfig,String deviceTypeCodeById,String specById);
class WarehouseTransferRuleConfigMapperProvider {
/**
* 用於複雜sql查詢提供sql拼接
*
* @param
* @return
*/
public String canAutoCreateSourceDetailList(WarehouseTransferRuleConfig warehouseTransferRuleConfig,String deviceTypeCodeById,String specById) {
//根據規則表數據拼接查詢一機一檔的sql
StringBuilder sql = new StringBuilder("select material_number,vehicle_vin_number,device_code,device_type_code,bl_division_code,region_code,device_model_code,device_spec_code,depositary_officer,storage_area,storage_province,storage_city,storage_address,placement_note,dispose_status,first_handover_date,handover_address_type from(select material_number,vehicle_vin_number,device_code,device_type_code,bl_division_code,region_code,device_model_code,device_spec_code,depositary_officer,storage_area,storage_province,storage_city,storage_address,placement_note,dispose_status,first_handover_date,handover_address_type from rmp_source_detail s where first_handover_status='Y' and depositary_officer is not null and handover_address_type is not null and bl_division_code is not null and device_spec_code is not null and dispose_status='01' and is_active='Y'");
if (warehouseTransferRuleConfig != null) {
//當前日期-定價日期＞7
sql.append(" and to_days(now()) - to_days(device_pricing_date)>7");
//設備規格
if (StringUtils.isNotBlank(specById)) {
String specStr="";
String[] split = specById.split(",");
for (int i = 0; i < split.length; i++) {
specStr=specStr+"'"+split[i]+"',";
}
specStr=specStr+specStr.substring(0,specStr.length()-1);
sql.append(" and device_spec_code in(" + specStr + ")");
}
//如未配置設備規格，則以設備類型爲條件
if (StringUtils.isBlank(specById)) {
String deviceTypeCodeSql="(select ds.device_type_code from(select device_type_code from rmp_warehouse_transfer_spec_config where id="+warehouseTransferRuleConfig.getRuleCode()+" and is_active='Y' limit 1)as ds)";
sql.append(" and device_type_code in(" + deviceTypeCodeSql + ")");
}
//過戶判斷
if (warehouseTransferRuleConfig.getTransferJudge() != null) {
sql.append(" and pass_judge=" + warehouseTransferRuleConfig.getTransferJudge());
}
//存放地類型
if (warehouseTransferRuleConfig.getHandoverAddressType() != null) {
sql.append(" and handover_address_type in(" + warehouseTransferRuleConfig.getHandoverAddressType() + ")");
}
sql=sql.append(") AS ts ");
//獲取預計整修成本的sql(不能爲0)
String estimateRepairCostsSql = "(select if(repair_budget='0',null,repair_budget)repair_budget from rmp_source_detail where material_number=ts.material_number)";
//獲取市場價的sql(不能爲0)
String marketPriceSql = "(select if(market_price='0',null,market_price)market_price from rmp3_price_adjustment_history_sheet where material_number=ts.material_number ORDER BY create_date DESC LIMIT 1)";
sql.append(" where ts.material_number in (select material_number from rmp_source_detail where 1=1 ");
//預計整修成本/市場全款價（區間始%）
if (warehouseTransferRuleConfig.getIntervalValueStart() != null) {
sql.append(" and repair_budget/" + estimateRepairCostsSql + ">" + (warehouseTransferRuleConfig.getIntervalValueStart() / 100));
}
//預計整修成本/市場全款價（區間止%）
if (warehouseTransferRuleConfig.getIntervalValueEnd() != null) {
sql.append(" and repair_budget/" + marketPriceSql + "<=" + (warehouseTransferRuleConfig.getIntervalValueEnd() / 100));
}
//條件（and or）
if (StringUtils.isNotBlank(warehouseTransferRuleConfig.getConditions())) {
sql.append(" " + warehouseTransferRuleConfig.getConditions() + " ");
}
if (warehouseTransferRuleConfig.getRepairCostsStart() != null || warehouseTransferRuleConfig.getRepairCostsEnd() != null) {
sql.append("(");
//預計整修成本始（萬）
if (warehouseTransferRuleConfig.getRepairCostsStart() != null) {
sql.append(" repair_budget>" + warehouseTransferRuleConfig.getRepairCostsStart());
}
//預計整修成本止（萬）
if (warehouseTransferRuleConfig.getRepairCostsEnd() != null && warehouseTransferRuleConfig.getRepairCostsStart() != null) {
sql.append(" and repair_budget<=" + warehouseTransferRuleConfig.getRepairCostsEnd());
}
if (warehouseTransferRuleConfig.getRepairCostsEnd() != null && warehouseTransferRuleConfig.getRepairCostsStart() == null) {
sql.append(" repair_budget<=" + warehouseTransferRuleConfig.getRepairCostsEnd());
}
sql.append(")");
}
sql.append(")");
System.out.println("打印sql=" + sql.toString());
}
return sql.toString();
}
}
後臺打印的sql語句：
SELECT
material_number,
vehicle_vin_number,
device_code,
device_type_code,
bl_division_code,
region_code,
device_model_code,
device_spec_code,
depositary_officer,
storage_area,
storage_province,
storage_city,
storage_address,
placement_note,
dispose_status,
first_handover_date,
handover_address_type
FROM
(
SELECT
material_number,
vehicle_vin_number,
device_code,
device_type_code,
bl_division_code,
region_code,
device_model_code,
device_spec_code,
depositary_officer,
storage_area,
storage_province,
storage_city,
storage_address,
placement_note,
dispose_status,
first_handover_date,
handover_address_type
FROM
rmp_source_detail s
WHERE
first_handover_status = 'Y'
AND depositary_officer IS NOT NULL
AND handover_address_type IS NOT NULL
AND bl_division_code IS NOT NULL
AND device_spec_code IS NOT NULL
AND dispose_status = '01'
AND is_active = 'Y'
AND to_days(
now()) - to_days( device_pricing_date )> 7
AND device_spec_code IN (
'50米-3橋-奔馳-國三',
'50米-4橋-五十鈴-國三',
'50米-4橋-奔馳-國三',
'50米-4橋-日野-國三',
'52米-3橋-奔馳-國五',
'52米-4橋-五十鈴-國三',
'52米-4橋-奔馳-國三',
'52米-4橋-奔馳-國四',
'52米-4橋-斯堪尼亞-國三',
'52米-4橋-日野-國三',
'53米-4橋-奔馳-國五',
'53米-4橋-斯堪尼亞-國五',
'54米-4橋-斯堪尼亞-國三',
'56米-4橋-奔馳-國三',
'56米-4橋-奔馳-國五',
'56米-4橋-奔馳-國四',
'56米-4橋-斯堪尼亞-國三',
'56米-4橋-斯堪尼亞-國五',
'56米-4橋-斯堪尼亞-國四',
'56米-4橋-解放-國五',
'56米-碳纖維-3橋-奔馳-國四',
'58米-5橋-斯堪尼亞-國三',
'58米-5橋-斯堪尼亞-國五',
'50米-3橋-奔馳-國三',
'50米-4橋-五十鈴-國三',
'50米-4橋-奔馳-國三',
'50米-4橋-日野-國三',
'52米-3橋-奔馳-國五',
'52米-4橋-五十鈴-國三',
'52米-4橋-奔馳-國三',
'52米-4橋-奔馳-國四',
'52米-4橋-斯堪尼亞-國三',
'52米-4橋-日野-國三',
'53米-4橋-奔馳-國五',
'53米-4橋-斯堪尼亞-國五',
'54米-4橋-斯堪尼亞-國三',
'56米-4橋-奔馳-國三',
'56米-4橋-奔馳-國五',
'56米-4橋-奔馳-國四',
'56米-4橋-斯堪尼亞-國三',
'56米-4橋-斯堪尼亞-國五',
'56米-4橋-斯堪尼亞-國四',
'56米-4橋-解放-國五',
'56米-碳纖維-3橋-奔馳-國四',
'58米-5橋-斯堪尼亞-國三',
'58米-5橋-斯堪尼亞-國五'
)
AND handover_address_type IN ( 1, 2, 4 )) AS ts
WHERE
ts.material_number IN (
SELECT
material_number
FROM
rmp_source_detail
WHERE
1 = 1
AND repair_budget /(
SELECT
IF
( market_price = '0', NULL, market_price ) market_price
FROM
rmp3_price_adjustment_history_sheet
WHERE
material_number = ts.material_number
ORDER BY
create_date DESC
LIMIT 1
)<= 0.3
AND ( repair_budget <= NULL ))
看到打印的sql大家應該也遇到同樣的需求，需要負責的查詢SQL或者新增的SQL吧，都可以採用上述方式👆
解釋說明和注意事項：
1)爲什麼不推薦這個時候使用xml呢？其實xml也可以達到效果，但是靈活性不高，例如for循環裏面切割字符再次拼接，而且編輯sql時容易出錯，項目改動xml文件還要重新啓動，而重新加載類可以不用重新啓動，搭配Jrebel熱加載使用，不知道熱加載的可以參考這篇文章https://blog.csdn.net/zeal9s/article/details/84204812
雖然說debug也可以做到實時部署，但是不穩定，而且遇到springboot項目，還要添加依賴才能實現，種種綜合來看xml方式在此不適合
2）
@SelectProvider提供自定義sql的註解
type：自定義SQL的類型（在這裏就是提供查詢的那個內部類WarehouseTransferRuleConfigMapperProvider）
method:該類的具體哪個方法提供sql
3）註解下面一行代表你需要的數據（數據字段不確定，可以用Map、List或者自定義Dto層接收）和參數（參數不確定建議用Map接受，或者List等，如多個參數，可在參數前面加@param註解，例如@param String sex,@param int age）但是我的沒加也能正常運作，可不加
List<SourceDetail> canAutoCreateSourceDetailList(WarehouseTransferRuleConfig warehouseTransferRuleConfig,String deviceTypeCodeById,String specById);
4）下面的類是Mapper層的內部類，注意 在此類不能注入其它mapper或者service對象，會導致注入對象失敗（已踩坑，具體原因尚且不知道），這也意味着所有的sql和邏輯層，必須在此類完成
class WarehouseTransferRuleConfigMapperProvider {
....
}
5）內部類中的方法名必須和註解@SelectProvider的說明保持一致，不然引用失敗
6）避免sql出現拼寫錯誤，最好初始化一個簡單查詢寫在最前面和最後面，。。。。。。
處再去處理複雜SQL拼接，例如
StringBuilder sql = new StringBuilder("select material_number,vehicle_vin_number,device_code,device_type_code,bl_division_code,region_code,device_model_code,device_spec_code,depositary_officer,storage_area,storage_province,storage_city,storage_address,placement_note,dispose_status,first_handover_date,handover_address_type from(select material_number,vehicle_vin_number,device_code,device_type_code,bl_division_code,region_code,device_model_code,device_spec_code,depositary_officer,storage_area,storage_province,storage_city,storage_address,placement_note,dispose_status,first_handover_date,handover_address_type from rmp_source_detail s where first_handover_status='Y' and depositary_officer is not null and handover_address_type is not null and bl_division_code is not null and device_spec_code is not null and dispose_status='01' and is_active='Y'");
。。。。。。
sql = sql.append(")");
7）這裏採用StringBuilder是提高拼接效率，也可以使用String方式的+=或者concat拼接
8）最後最好打印一下sql，方便排查sql錯誤可複製到數據庫運行
9）紀念多次子查詢博主踩的坑
①子查詢獲取最外層查詢的值：可以將最外層的查詢再包裹一層，給這個視圖取個別名，子查詢使用別名.字段的方式獲取，如果直接獲取最外層數據你要想想sql的執行順序哦)
②子查詢不能使用limit關鍵字查詢（本來是想用limit提高查詢效率，sql本身沒錯不料執行出錯，解決方法請看https://blog.csdn.net/zeal9s/article/details/99739003）
③使用關鍵詞in查詢時，出現數據偏差，原因是拼接這個sql時
AND device_spec_code IN (
'50米-3橋-奔馳-國三',
'50米-4橋-五十鈴-國三',
'50米-4橋-奔馳-國三',
'50米-4橋-日野-國三',
'52米-3橋-奔馳-國五',
)
，java代碼是
sql = sql.append(" and device_spec_code in(" + specStr + ")");
specStr作爲字符串變量，它的值是沒有加上引號的，所以拼接的時候要重新加上引號，不加引號sql不會報錯，但是數據不對
50米-3橋-奔馳-國三,50米-4橋-五十鈴-國三
④拼接字符串時一定要注意變量重新賦值，也可以採用concat和StringBuilder的append方法（不用重新賦值）
specStr=specStr+specStr.substring(0,specStr.length()-1); ✔️
specStr.substring(0,specStr.length()-1); ❌
10）每一次拼接的註釋最好寫上，方便維護。防止幾天之後，自己都不知道這寫的什麼，又要重新浪費時間閱讀代碼
12）除了查詢@SelectProvider還有@InsertProvider等用法可研究
11）技術多多實踐啦，把業務和技術結合起來才能解決實際問題哦~
說在最後的話：編寫實屬不易，若喜歡或者對你有幫助記得點贊+關注或者收藏哦~