# 增查改删 API

如 [代码生成](https://3ks.gitbook.io/ent-zh_cn/dai-ma-sheng-cheng/code-gen) 部分描述的那样，定义好模式后，运行 `entc` 可以生成以下内容

* 用于和图（数据库）交互的 `Client` 和 `Tx`. 
* 每个模式的增查改删（CRUD）构建器，查看 [增查改删API](https://3ks.gitbook.io/ent-zh_cn/dai-ma-sheng-cheng/crud) 详情。
* 每个模式的实体 (Go struct).
* 包含用于和构建器交互的常量和条件查询方法。
* 为 SQL 提供的 `migrate` 包. 查看 [数据库迁移](https://3ks.gitbook.io/ent-zh_cn/qian-yi/migrate) 详情。

## 创建一个客户端

**MySQL**

```go
package main

import (
    "log"

    "<project>/ent"

    _ "github.com/go-sql-driver/mysql"
)

func main() {
    client, err := ent.Open("mysql", "<user>:<pass>@tcp(<host>:<port>)/<database>?parseTime=True")
    if err != nil {
        log.Fatal(err)
    }
    defer client.Close()
}
```

**SQLite**

```go
package main

import (
    "log"

    "<project>/ent"

    _ "github.com/mattn/go-sqlite3"
)

func main() {
    client, err := ent.Open("sqlite3", "file:ent?mode=memory&cache=shared&_fk=1")
    if err != nil {
        log.Fatal(err)
    }
    defer client.Close()
}
```

**Gremlin (AWS Neptune)**

```go
package main

import (
    "log"

    "<project>/ent"
)

func main() {
    client, err := ent.Open("gremlin", "http://localhost:8182")
    if err != nil {
        log.Fatal(err)
    }
}
```

## 创建

创建一个实体。

**Save** 创建一个用户.

```go
a8m, err := client.User.    // UserClient.
    Create().                // User create builder.
    SetName("a8m").            // Set field value.
    SetNillableAge(age).    // Avoid nil checks.
    AddGroups(g1, g2).        // Add many edges.
    SetSpouse(nati).        // Set unique edge.
    Save(ctx)                // Create and return.
```

**SaveX** 创建一个用户；不同于 **Save**, **SaveX** 遇到错误时会引起 panics.

```go
pedro := client.Pet.    // PetClient.
    Create().            // User create builder.
    SetName("pedro").    // Set field value.
    SetOwner(a8m).        // Set owner (unique edge).
    SaveX(ctx)            // Create and return.
```

## 更新

更新一个数据库返回的实体。

```go
a8m, err = a8m.Update().    // User update builder.
    RemoveGroup(g2).        // Remove specific edge.
    ClearCard().            // Clear unique edge.
    SetAge(30).                // Set field value
    Save(ctx)                // Save and return.
```

## 根据 ID 更新

根据 ID 更新一个实体。

```go
pedro, err := client.Pet.    // PetClient.
    UpdateOneID(id).        // Pet update builder.
    SetName("pedro").        // Set field name.
    SetOwnerID(owner).        // Set unique edge, using id.
    Save(ctx)                // Save and return.
```

## 更新多个

根据条件过滤更新多个实体。

```go
n, err := client.User.            // UserClient.
    Update().                    // Pet update builder.
    Where(                        //
        user.Or(                // (age >= 30 OR name = "bar") 
            user.AgeEQ(30),     //
            user.Name("bar"),    // AND
        ),                        //  
        user.HasFollowers(),    // UserHasFollowers()  
    ).                            //
    SetName("foo").                // Set field name.
    Save(ctx)                    // exec and return.
```

Query edge-predicates.

```go
n, err := client.User.            // UserClient.
    Update().                    // Pet update builder.
    Where(                        // 
        user.HasFriendsWith(    // UserHasFriendsWith (
            user.Or(            //   age = 20
                user.Age(20),    //      OR
                user.Age(30),    //   age = 30
            )                    // )
        ),                         //
    ).                            //
    SetName("a8m").                // Set field name.
    Save(ctx)                    // exec and return.
```

## 查询

Query The Graph. 查询有粉丝的用户。

```go
users, err := client.User.        // UserClient.
    Query().                    // User query builder.
    Where(user.HasFollowers()).    // filter only users with followers.
    All(ctx)                    // query and return.
```

获取某个用户的粉丝列表；从图中的某个节点开始图遍历。

```go
users, err := a8m.
    QueryFollowers().
    All(ctx)
```

获取某个用户的所有粉丝的所有宠物。

```go
users, err := a8m.
    QueryFollowers().
    QueryPets().
    All(ctx)
```

获取所有宠物的名字。

```go
names, err := client.Pet.
    Query().
    Select(pet.FieldName).
    Strings(ctx)
```

获取所有宠物的名字和年龄。

```go
var v []struct {
    Age  int    `json:"age"`
    Name string `json:"name"`
}
err := client.Pet.
    Query().
    Select(pet.FieldAge, pet.FieldName).
    Scan(ctx, &v)
if err != nil {
    log.Fatal(err)
}
```

你可以在 [遍历](https://3ks.gitbook.io/ent-zh_cn/dai-ma-sheng-cheng/traversals) 找到更多遍历的高级用法。

## 删除

删除一个实体。

```go
err := client.User.
    DeleteOne(a8m).
    Exec(ctx)
```

Delete by ID.

```go
err := client.User.
    DeleteOneID(id).
    Exec(ctx)
```

## 删除多个

根据条件过滤删除多个实体。

```go
err := client.File.
    Delete().
    Where(file.UpdatedAtLT(date))
    Exec(ctx)
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://3ks.gitbook.io/ent-zh_cn/dai-ma-sheng-cheng/crud.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.