```
In MyBatis, if you want to create a select query that considers only the non-null fields in an object, you can use `<if>` tags in the XML mapper file to construct a dynamic query. 

Here's an example using a hypothetical `` object. Assume that `` has fields: `id`, `name`, and `email`.

```xml
<select id="selectBySelective" parameterType="com.yourpackage." resultType="com.yourpackage.">
    SELECT *
    FROM 
    WHERE 1=1
    <if test="id != null">
        AND id = #{id}
    </if>
    <if test="name != null">
        AND name = #{name}
    </if>
    <if test="email != null">
        AND email = #{email}
    </if>
</select>
```

In the example above, if you pass a `` object where `id` and `name` are not null, but `email` is null, the resulting SQL will be:

```sql
SELECT * FROM  WHERE 1=1 AND id = #{id} AND name = #{name}
```

This way, the query is flexible and will only use the fields that are not null in the parameter object. 

Remember, `parameterType` attribute in the select tag points to your Java object, and `resultType` is the type of objects returned by the query. Both should be fully qualified names (i.e., including the package). 

Please replace `com.yourpackage.` with your actual Java object's fully qualified name.


Sure, if you'd like to select only certain fields instead of all fields (SELECT *), you just need to specify those fields in your select statement. For instance, let's consider the same `` object with `id`, `name`, and `email` fields, but this time you want to select only `id` and `name`.

Here is how you can modify the XML mapper file:

```xml
<select id="selectBySelective" parameterType="com.yourpackage." resultType="com.yourpackage.">
    SELECT id, name
    FROM 
    WHERE 1=1
    <if test="id != null">
        AND id = #{id}
    </if>
    <if test="name != null">
        AND name = #{name}
    </if>
</select>
```

In the SQL query, you replace `*` with the actual columns that you want to select, in this case, `id` and `name`.

Please note that, in this scenario, the `resultType` should be a class that contains only the `id` and `name` fields, or you should handle the returned fields correctly in your Java code.

As before, replace `com.yourpackage.` with your actual Java object's fully qualified name.


If you want to add pagination to your SQL queries in MyBatis, you need to use the `LIMIT` and `OFFSET` clauses. 

You need two parameters for this: one for the number of records per page (`pageSize`), and another for the page number (`pageNum`). 

Here is an example:

```xml
<select id="selectBySelective" parameterType="map" resultType="com.yourpackage.">
    SELECT id, name
    FROM 
    WHERE 1=1
    <if test="id != null">
        AND id = #{id}
    </if>
    <if test="name != null">
        AND name = #{name}
    </if>
    LIMIT #{pageSize} OFFSET #{pageNum} * #{pageSize}
</select>
```

In this example, the parameter type is now a `map` so that you can pass in the `id`, `name`, `pageSize`, and `pageNum` parameters. When you call this method in your Java code, you would pass in a Map with these keys and their corresponding values.

Please replace `com.yourpackage.` with your actual Java object's fully qualified name.

Also note that `LIMIT #{pageSize} OFFSET #{pageNum} * #{pageSize}` allows for pagination, where `pageSize` is the number of records per page and `pageNum` is the page number (starting from 0). 

Here's an example of how you might call this method in your Java code:

```java
Map<String, Object> params = new HashMap<>();
params.put("id", 1);
params.put("name", "1");
params.put("pageSize", 10);
params.put("pageNum", 0);
List<> s = sqlSession.selectList("selectBySelective", params);
```

This will return the first 10 s (0-9) with `id` equal to 1 and `name` equal to '1'. If you want the next page, you would increment `pageNum` by 1.

Again, this assumes that the page numbers are zero-based. If you want them to be one-based, you would need to adjust the `OFFSET` calculation accordingly.

Batch add

Sure! If you want to perform a batch insert operation using MyBatis, you can do it by using a `foreach` element in your mapper XML. Here's a simple example that demonstrates how to do it with a hypothetical `` class having fields `id`, `name`, and `email`.

```xml
<insert id="insertBatch" parameterType="java.util.List">
    INSERT INTO  (id, name, email)
    VALUES 
    <foreach collection="list" item="item" index="index" separator=",">
        (#{item.id}, #{item.name}, #{item.email})
    </foreach>
</insert>
```

In this example, `parameterType` is `java.util.List`, indicating that this method expects a List of `` objects as its argument. The `foreach` tag iterates through this list. For each `` object in the list (referred to as `item`), it generates a part of the SQL statement that inserts the `id`, `name`, and `email` of the `` into the `` table.

You would call this method in your Java code by passing a List of `` objects to it. Here's an example:

```java
List<> s = new ArrayList<>();
s.add(new (1, "name1", "email1"));
s.add(new (2, "name2", "email2"));
// ... Add as many s as you want
sqlSession.insert("insertBatch", s);
```

This example assumes that your `` class has a constructor that accepts `id`, `name`, and `email` as arguments. Adjust the code accordingly if this is not the case.

Please note that the batch operation's performance also depends on the JDBC driver and the database you are using. If you are expecting to perform very large batch operations, you should consider other factors such as transaction management and commit sizes.

List<> s = new ArrayList<>();
s.add(new (1, "name1", "email1"));
s.add(new (2, "name2", "email2"));
 here need foreach

No, in the given Java code, a `foreach` loop is not required to add elements to the `s` list. However, if you have a larger number of s or if the s are coming from another data structure, you might use a `foreach` loop. 

Here's an example, let's assume we have a list of names and emails, and we're assigning ids in increasing order starting from 1:

```java
List<String> names = Arrays.asList("name1", "name2", "name3");
List<String> emails = Arrays.asList("email1", "email2", "email3");

List<> s = new ArrayList<>();
int id = 1;

for(int i = 0; i < names.size(); i++) {
    s.add(new (id, names.get(i), emails.get(i)));
    id++;
}
```

In this example, a for loop is used to go through each name and email, create a new `` object with an id, name, and email, and then add it to the `s` list.

In the context of the batch insert, the `foreach` tag is used in the MyBatis XML mapper file to generate the SQL for each `` object in the list. The list is passed to the `sqlSession.insert()` method, and MyBatis handles the iteration over the list.

Batch update

To perform a batch update in MyBatis, you can use the `foreach` tag in a similar way as with the batch insert. Here's an example of how to do it using a hypothetical `` object with fields `id`, `name`, and `email`:

```xml
<update id="updateBatch" parameterType="java.util.List">
    <foreach collection="list" item="item" index="index" separator=";">
        UPDATE 
        SET 
        name = #{item.name},
        email = #{item.email}
        WHERE id = #{item.id}
    </foreach>
</update>
```

In this example, `parameterType` is `java.util.List`, which means this method expects a List of `` objects as its parameter. The `foreach` tag iterates over this list. For each `` object in the list (referred to as `item`), it generates a part of the SQL statement that updates the `name` and `email` fields of the corresponding record (where `id` matches).

You can call this method in your Java code like this:

```java
List<> s = new ArrayList<>();
s.add(new (1, "newname1", "newEmail1"));
s.add(new (2, "newname2", "newEmail2"));
// ... add as many s as you want
sqlSession.update("updateBatch", s);
```

This example assumes that your `` class has a constructor that accepts `id`, `name`, and `email` as arguments. If this is not the case, you would need to adjust the code accordingly.

Note: The separator `;` is used to separate multiple SQL statements. Some databases do not support multiple statements in a single transaction. Please check if your database and JDBC driver support this feature. If not, you may need to perform each update operation in a separate transaction, which can impact performance.

Batch select

In MyBatis, batch select (selecting multiple rows based on a list of parameters) can be implemented using the `<foreach>` tag in your XML mapper file. Here's a simple example with a hypothetical `` object, where you want to select multiple s based on a list of `ids`:

```xml
<select id="selectBatch" parameterType="java.util.List" resultType="com.yourpackage.">
    SELECT id, name, email
    FROM 
    WHERE id IN 
    <foreach collection="list" item="item" index="index" open="(" close=")" separator=",">
        #{item}
    </foreach>
</select>
```

In this example, the parameter type is a `java.util.List`, indicating that this method expects a List of `ids` as its argument. The `<foreach>` tag iterates over this list. For each `id` in the list, it generates part of the SQL statement.

Here is how you would call this method in your Java code:

```java
List<Integer> ids = Arrays.asList(1, 2, 3);
List<> s = sqlSession.selectList("selectBatch", ids);
```

This will return a list of `` objects whose `id` field matches any of the `ids` in the list that you passed to the method.

Remember to replace `com.yourpackage.` with your actual Java object's fully qualified name.


    <foreach collection="list" item="item" index="index" open="(" close=")" separator=",">
        #{item}
    </foreach>
 how to use "list" param in java

The `list` parameter in the `<foreach>` tag in the MyBatis XML mapper refers to the parameter you pass into the method when you call it from your Java code. Here's how you would use it in Java:

```java
List<Integer> ids = Arrays.asList(1, 2, 3, 4, 5); // The list of IDs you want to select
List<> s = sqlSession.selectList("selectBatch", ids);
```

In this case, "selectBatch" is the `id` of the `<select>` tag in the XML mapper file, and `ids` is the List of `id` values you want to select. `ids` corresponds to the `list` parameter in the XML file.

When you call `sqlSession.selectList("selectBatch", ids)`, MyBatis executes the SQL query specified in the `selectBatch` method in the XML mapper file, with `list` replaced by the `ids` List. The `foreach` loop in the XML file iterates over each item in `list` (i.e., `ids`), adding each `id` value to the `IN` clause in the SQL query. The resulting list of `` objects is then returned by the `selectList()` method.

Please white Batch delete mybatis xml 

Batch deleting in MyBatis is quite similar to batch selecting. You can use the `<foreach>` tag to iterate over a list of IDs for deletion. Here's an example using a hypothetical `` table:

```xml
<delete id="deleteBatch" parameterType="java.util.List">
    DELETE FROM 
    WHERE id IN 
    <foreach collection="list" item="item" index="index" open="(" close=")" separator=",">
        #{item}
    </foreach>
</delete>
```

In this case, the `parameterType` is `java.util.List`, indicating this method expects a List of `ids` as its argument. The `<foreach>` tag iterates over this list. For each `id` in the list, it generates part of the SQL statement.

You can call this method in your Java code like this:

```java
List<Integer> ids = Arrays.asList(1, 2, 3);
sqlSession.delete("deleteBatch", ids);
```

This will delete the `` records whose `id` field matches any of the `ids` in the list that you passed to the method.

Remember, this operation is permanent and the records deleted cannot be recovered. Be careful while using delete operations. Also, please consider the impact of deleting records on related tables due to foreign key relationships.


batch add，how to get input parameters from the front end

Receiving input parameters for a batch add operation from a front-end application typically involves making a HTTP request (usually a POST or PUT request) to your server-side application. 

Here's a brief example of how you might handle this using Spring Boot for the server-side and a JavaScript-based front-end.

Server-side (Spring Boot):

```java
@RestController
@RequestMapping("/s")
public class Controller {

    @Autowired
    private Service Service;

    @PostMapping("/batch")
    public ResponseEntity<?> addsBatch(@RequestBody List<> s) {
        Service.addsBatch(s);
        return ResponseEntity.ok().build();
    }
}
```

In this example, Spring's `@RestController` and `@RequestMapping` annotations define a REST API controller. The `addsBatch` method uses the `@PostMapping` annotation to handle POST requests to the "/s/batch" URL. 

The `@RequestBody` annotation tells Spring to convert the JSON payload of the HTTP request into a List of `` objects.

Client-side (JavaScript):

```javascript
const s = [
    { id: 1, name: 'name1', email: 'email1' },
    { id: 2, name: 'name2', email: 'email2' },
    //... more s
];

fetch('http://localhost:8080/s/batch', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify(s),
});
```

In this JavaScript example, the `fetch` function is used to make a POST request to the "/s/batch" URL (assuming your server-side application is running on localhost at port 8080). The `s` array is converted to a JSON string and included in the body of the request.

Remember that error handling, CORS settings, and the like have been omitted from these examples for simplicity. Also, consider using a more robust solution for state management and HTTP requests in a larger front-end application, such as Redux or Axios in a React application.

Front end may input a json data

Yes, typically in a front-end to back-end communication, JSON (JavaScript Object Notation) is used as the data format. It's lightweight and easy to work with in JavaScript.

Here's an example of how you might send JSON data from a JavaScript front-end to a Spring Boot back-end:

Client-side (JavaScript):

```javascript
const s = [
    { id: 1, name: 'name1', email: 'email1' },
    { id: 2, name: 'name2', email: 'email2' },
    //... more s
];

fetch('http://localhost:8080/s/batch', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify(s),
});
```

In this JavaScript example, the `fetch` function is used to make a POST request to the "/s/batch" URL (assuming your server-side application is running on localhost at port 8080). The `s` array is converted to a JSON string with `JSON.stringify` and included in the body of the request.

Server-side (Spring Boot):

```java
@RestController
@RequestMapping("/s")
public class Controller {

    @Autowired
    private Service Service;

    @PostMapping("/batch")
    public ResponseEntity<?> addsBatch(@RequestBody List<> s) {
        Service.addsBatch(s);
        return ResponseEntity.ok().build();
    }
}
```

In the Spring Boot controller, the `@RequestBody` annotation tells Spring to convert the JSON payload of the HTTP request into a List of `` objects. 

These examples assume that you have a `` class in your Java code that corresponds to the JSON objects in the `s` array, with `id`, `name`, and `email` fields. If the JSON data is different, you would need to adjust the `` class or the method of parsing the JSON data accordingly.

what about const s = {data: [
    { id: 1, name: 'name1', email: 'email1' },
    { id: 2, name: 'name2', email: 'email2' },
    //... more s
]};

If your JSON data is structured that way, with the `s` array contained inside a `data` object, you would need to slightly modify your server-side code to handle it.

You can create a new class, say `Batch`, which contains a List of `` objects, like this:

```java
public class Batch {
    private List<> data;

    // getters and setters
}
```

Then, in your `Controller`, you would change the parameter of the `addsBatch` method to `Batch Batch`:

```java
@RestController
@RequestMapping("/s")
public class Controller {

    @Autowired
    private Service Service;

    @PostMapping("/batch")
    public ResponseEntity<?> addsBatch(@RequestBody Batch Batch) {
        Service.addsBatch(Batch.getData());
        return ResponseEntity.ok().build();
    }
}
```

In this example, the `@RequestBody` annotation tells Spring to convert the JSON payload of the HTTP request into a `Batch` object.

The client-side JavaScript code would remain the same:

```javascript
const s = {
    data: [
        { id: 1, name: 'name1', email: 'email1' },
        { id: 2, name: 'name2', email: 'email2' },
        //... more s
    ]
};

fetch('http://localhost:8080/s/batch', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify(s),
});
```

This will send a POST request with the JSON payload as the body. The payload will be converted into a `Batch` object on the server-side, and the `data` List will be passed to the `addsBatch` method in the `Service`.

What about batch update?

The process for a batch update with the provided JSON structure would be similar to the batch add example.

Firstly, the JSON structure from the client-side (JavaScript):

```javascript
const s = {
    data: [
        { id: 1, name: 'newname1', email: 'newEmail1' },
        { id: 2, name: 'newname2', email: 'newEmail2' },
        //... more s
    ]
};

fetch('http://localhost:8080/s/batchUpdate', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify(s),
});
```

Here, we are making a POST request to the "/s/batchUpdate" URL with the updated  data.

The server-side (Spring Boot) code would look like this:

```java
@RestController
@RequestMapping("/s")
public class Controller {

    @Autowired
    private Service Service;

    @PostMapping("/batchUpdate")
    public ResponseEntity<?> updatesBatch(@RequestBody Batch Batch) {
        Service.updatesBatch(Batch.getData());
        return ResponseEntity.ok().build();
    }
}
```

In the `Controller`, we have an `updatesBatch` method which accepts a `Batch` object. This object is automatically created by Spring Boot from the JSON payload thanks to the `@RequestBody` annotation. We extract the list of s with `Batch.getData()` and pass it to the `updatesBatch` method of the `Service`.

The `Service` should then perform the batch update operation. This operation could utilize the MyBatis XML mapper file you've created for batch update operations. 

Again, make sure that the fields in the JSON objects align with the properties of the `` objects in your Java code. Also, ensure that the REST endpoint (in this case "/s/batchUpdate") matches the one you're calling from the front end.

What about batch delete?

In the case of batch delete, usually only the identifiers (IDs) for the entities to delete are sent from the front end. Here's how you would do this:

Client-side (JavaScript):

```javascript
const s = {
    data: [1, 2, 3, 4, 5] // ids of s to delete
};

fetch('http://localhost:8080/s/batchDelete', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify(s),
});
```

In this JavaScript example, we are making a POST request to the "/s/batchDelete" URL, with the list of IDs to delete in the body of the request.

Server-side (Spring Boot):

```java
@RestController
@RequestMapping("/s")
public class Controller {

    @Autowired
    private Service Service;

    @PostMapping("/batchDelete")
    public ResponseEntity<?> deletesBatch(@RequestBody IdBatch idBatch) {
        Service.deletesBatch(idBatch.getData());
        return ResponseEntity.ok().build();
    }
}
```

In the `Controller`, we have a `deletesBatch` method which accepts a `IdBatch` object. `IdBatch` is a class you'd define which simply contains a List of integers. 

The `@RequestBody` annotation tells Spring to convert the JSON payload of the HTTP request into an `IdBatch` object. We extract the list of IDs with `idBatch.getData()` and pass it to the `deletesBatch` method in the `Service`.

The `Service` should then perform the batch delete operation. This operation could utilize the MyBatis XML mapper file you've created for batch delete operations.

Remember, deletion is a permanent operation, and the deleted records can't be recovered. Always ensure the accuracy and validity of the IDs being deleted.

What about batch query?

The process for a batch query (select) operation with a JSON structure would be similar to the previous examples. You will typically send the list of identifiers (IDs) for the entities you want to select from the front-end.

Firstly, the JSON structure from the client-side (JavaScript):

```javascript
const s = {
    data: [1, 2, 3, 4, 5] // ids of s to select
};

fetch('http://localhost:8080/s/batchSelect', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
    },
    body: JSON.stringify(s),
});
```

Here, we are making a POST request to the "/s/batchSelect" URL with the IDs of the s we want to select.

The server-side (Spring Boot) code would look like this:

```java
@RestController
@RequestMapping("/s")
public class Controller {

    @Autowired
    private Service Service;

    @PostMapping("/batchSelect")
    public ResponseEntity<List<>> selectsBatch(@RequestBody IdBatch idBatch) {
        List<> s = Service.selectsBatch(idBatch.getData());
        return ResponseEntity.ok(s);
    }
}
```

In the `Controller`, we have a `selectsBatch` method which accepts an `IdBatch` object. This object is automatically created by Spring Boot from the JSON payload thanks to the `@RequestBody` annotation. We extract the list of IDs with `idBatch.getData()` and pass it to the `selectsBatch` method of the `Service`.

The `Service` should then perform the batch select operation, which could utilize the MyBatis XML mapper file you've created for batch select operations. The list of `` objects returned by the `Service` is then sent back to the client in the HTTP response.

Write batch update xml

To write a batch update using MyBatis, you can use the `<foreach>` tag to iterate over the list of s you're updating. You need to be careful because some databases do not support batch operations directly with MyBatis. However, you can do a workaround like this:

```xml
<update id="updateBatch" parameterType="java.util.List">
    <foreach collection="list" item="" separator=";">
        UPDATE 
        SET
        name = #{.name},
        email = #{.email}
        WHERE id = #{.id}
    </foreach>
</update>
```

In this XML, we're iterating over a list of `` objects. For each ``, we generate an update statement that sets the `name` and `email` fields based on the values in the `` object, where the `id` matches the `id` in the `` object.

You can then use this MyBatis mapper method in your Java code as follows:

```java
List<> s = new ArrayList<>();
s.add(new (1, "newname1", "newEmail1"));
s.add(new (2, "newname2", "newEmail2"));
//... add more s
sqlSession.update("updateBatch", s);
```

This example assumes that you have a `` class with `id`, `name`, and `email` properties, and that the values you're updating are stored in the `` objects in the `s` list. Please adjust the field names and values according to your database schema and application requirements.

Remember, you need to be aware of the transaction scope. If you have a large batch, it may be necessary to break it into smaller batches and manage transactions to prevent data inconsistency in case of failures during the update process.

The `IdBatch` class is a simple Java class that would hold a list of integers, representing the IDs. This class is used to map the JSON payload coming from the front-end to a Java object on the back-end.

Here's how you could define it:

```java
import java.util.List;

public class IdBatch {
    private List<Integer> data;

    public List<Integer> getData() {
        return data;
    }

    public void setData(List<Integer> data) {
        this.data = data;
    }
}
```

This class contains a `List<Integer>` to hold the IDs (`data`), and getter and setter methods to manipulate this list. This class is used with the `@RequestBody` annotation in the controller methods to automatically convert the JSON payload from the front-end into a `IdBatch` object.

For instance, if the front-end sends this JSON payload: `{ "data": [1, 2, 3] }`, Spring Boot would create an `IdBatch` object where `data` is a list containing the integers 1, 2, and 3.
```