What's the difference between # {} and ${} in MyBatis

This article mainly introduces the difference between # {} and ${} in MyBatis, which has a certain reference value. Interested friends can refer to it. I hope you can learn a lot after reading this article.

Preface

In the mapping configuration file of MyBatis, there are two ways to pass parameters dynamically:

1. # {} placeholder

2. ${} splicer

# {} and ${}

Difference 1

# {} is the parameter placeholder?, that is, sql precompilation

${} is string substitution, that is, sql stitching

Difference 2.

# {}: dynamic parsing-> precompilation-> execution

${}: dynamic parse-> compile-> execute

Difference 3.

The variable substitution of # {} is in DBMS

The variable substitution of ${} is outside of DBMS

Difference 4.

After variable replacement, the variable corresponding to # {} is automatically enclosed in single quotation marks''

After variable replacement, the variable corresponding to ${} will not be enclosed in single quotation marks''

Difference 5.

# {} prevents sql injection

${} cannot prevent sql injection

# {} and ${} instances: suppose the passed parameter is 1 instance step 1 # {}: select * from t_user where uid=# {uid} ${}: select * from t_user where uid='${uid} 'instance step 2 # {}: select * from t_user where uid=? ${}: select * from t_user where uid=' 1' instance step 3 # {}: select * from t_user where uid='1 instance ${}: select * from Values in curly braces of t_user where uid='1s # {} and ${}

The case of a single parameter

# {}

${}

Case of multiple parameters # {}

${}

# {} and ${} tips and suggestions in use

1. Whether it is a single parameter or multiple parameters, the annotation @ Param (") is recommended.

2. Use # {} where you can, and use ${} less or less

3. When the table name is used as a parameter, you must use ${}. Such as: select * from ${tableName}

4. When order by, you must use ${}. Such as: select * from t_user order by ${columnName}

5. If you use # {} in the name of the list, you will directly report an error; sorting with # {} after order by will not take effect.

6. When using ${}, pay attention to when to add or not add single quotation marks, that is, ${} and'${}'. In general, single quotation marks are required when the field type is char or varchar

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